Home

QUÍMICA EXPERIMENTAL III

Contents

1. Introducci n a la ciencia e ingenier a de los materiales Vol II Ed Revert Barcelona 2000 21 M J Geselbracht A M Cappellari A B Ellis M A Rzeznik B J Johnson J Chem Ed 1994 71 8 696 703 ver p ginas siguientes 22 Rare Earth Iron Garnets Their Synthesis and Magnetic Properties Margret J Geselbracht Ann M Cappellari and Arthur B Ellis University of Wisconsin Madison Madison WI 53706 Maria A Rzeznik University of California Berkeley Berkeley CA 94720 Brian J Johnson St John s University St Joseph MN 56374 The interaction of solids with magnetic fields is a topic that is discussed rarely in introductory chemistry courses This occurs in spite of the proliferation of magnetic mate rials in today s society including magnetic recording media and data storage We believe that a presentation of the magnetic properties of solids fits well into the general chemistry course because it provides a vehicle for discuss ing the existence of electrons the electronic configurations of ions and the role of solid state structure Our experi ment involving the preparation and study of a series of magnetic garnets with the composition Y Gdy FesOya 0 lt x lt 3 that illustrates these topics follows In addition this experiment provides the opportunity to discuss the differ ent types of magnetism in solids to perform some chemis try using rare earth elements and to learn abo
2. 1 M The hot yellow filtrate is treated immediately with 15 mL of concen trated HBr A copious fine yellow crystalline precipitate forms After cooling to room temperature this is collected on a frit under suction washed with cold 1 1 methanol water metha nol then ether and dried at the pump and if required in a vacuum desiccator yield 1 95g 55 Characterization of the Macrobicyclic Complex Electronic Spectrum The Co dinosar 3 complex has ab sorption maxima in the visible region at 475 nm e 148 M cm and 342 nm e 133 typical of an octahedral saturated CoNg chromophore and similar to the Co en 33 precursor 466 nm e 75 338 nm e 68 Figure 1 Infrared Spectra The fingerprint pattern of the macrobicyclic ligand is quite different from that of the Co en a Br3 precursor The characteristically strong ab sorbance of NOx can be seen at 1560 cm in a KBr disc spectrum of the macrobicyclic complex NMR Spectra The 1 C NMR spectrum JEOL FX 60 spectrometer D20 shifts relative to dioxan ve downfield illustrates the essentially D3 symmetry in the macrobicyclic complex Three signals are observed at 11 3 ppm due to CH gt groups of the en ring residues 15 1 ppm due to CHp groups of the capping units and a resonance at 21 4 ppm due to the tertiary gt C NO of the caps For Co en 33 a single resonance occurs at 21 8 ppm The high symmetry of the macrobicycle is also evident fr
3. 2 C5H5 gt C1o0H10 so rec DO 44 Fulvalene H Structures which Fe were originally proposed M C H Fe C H H 1952 E O Fischer Double cone structure based on X ray structural analysis compare ce the electron density contour lines X7 diamagnetism chemical behavior a 1952 G Wilkinson R B Woodward Sandwich structure based on IR spectroscopy diamagnetism dipole moment 0 Woodward The cyclopentadienyl rings of Fe C Hs are amenable to electrophilic substi tutions This similarity to the aromatic behavior of benzene led to the trivial name ferrocene later being extended to the designation metallocenes for compounds M y C sH in gener al 15 4 3 1 Binary Cyclopentadienyl Transition Metal Complexes PREPARATION 1 Metal Salt Cyclopentadienyl Reagent Dicyclopentadiene has first to be cracked in a retro Diels Alder reaction to give monomeric CsH Cyclopentadiene is a weak acid pK x 15 it can be deprotonated by strong bases or by alkali metals Cyclopentadienylsodium NaCp is the most common reagent for the introduction of cyclopentadienyl ligands 42 328 15 n Donor n Acceptor Ligands Ferrocene ruthenocene and osmocene are susceptible to electrophilic substitution Com pared to benzene ferrocene reacts 3 x 10 times faster PSV Fe Fe Fe The electrophile should not be an oxidizing agent as sub
4. R et al Laboratory Experiments in Organic Chemistry 7th Ed Macmillan Publishing Co New York 1979 p 452 6 Wade L G J CHEM EDUC 55 208 1978 7 Bozak R E J CHEM EDUC 43 73 1966 8 Herz J E J CHEM EDUC 43 599 1966 9 Bohen J M et al J CHEM EDUC 50 367 1973 10 Gilbert J C and Monti S A J CHEM EDUC 50 369 1973 11 Haworth D T and Liu T J J CHEM EDUC 53 730 1976 12 Haworth D I and Liu T J J Chromatogr 14 519 1978 13 Colin H and Guiochon G J Chramatngr 141 289 LITT 14 Glaor R and Johnson E L J Chromatogr 15 419 1977 45 7 EFECTO PLANTILLA La coordinaci n de ligandos a metales de transici n permite dirigir estereoqu micamente su reactividad dando lugar a productos diferentes a los que se obtendr an sin la participaci n del metal Un buen ejemplo de esto es el conocido efecto plantilla Los ligandos coordinados a un metal reaccionan dando lugar a un nuevo ligando que se adapta a la geometr a definida por el metal 7 A S ntesis de complejos macroc clicos de n quel y cobre En el ejemplo que se va a realizar la condensaci n de una diamina y una dicetona en presencia de acetato de n quel da lugar a un macrociclo que act a como ligando obtendr a el ciclo 3 de la Figura 1 quelato en torno a tomo de n quel Si la reacci n se hiciera en ausencia del metal se NH O 0 ne
5. con una estructura tipo sandwich en la que los dos anillos ciclopentadieno tienen car cter arom tico dio lugar a un desarrollo importante de la qu mica organomet lica La pr ctica consiste en la preparaci n de ferroceno para despu s realizar una sustituci n electrof lica sobre uno de los anillos ciclopentadieno aislando acetilferroceno Procedimiento experimental 6 A Obtenci n de ferroceno En un matraz de 100 mL equipado con un refrigerante se ponen bajo atm sfera de nitr geno 5 2 g de NaOH triturado y 50 mL de ter et lico A la suspensi n bien agitada se a aden 5 6 mL de ciclopentadieno reci n destilado y despu s de 20 minutos una disoluci n formada por 6 6 g de FeCl 4H O en 25 mL de dimetilsulf xido gota a gota La reacci n que se produce es exot rmica y se pone espont neamente a reflujo Finalizada la adici n se mantiene la agitaci n durante 30 minutos m s La fase l quida contenida en el matraz se decanta y el residuo negro se trata con 30 mL de ter La fase l quida decantada se junta con la fase et rea y el combinado se trata primero con HCl 2M 2 x 40 mL y despu s con agua 2 x 40 mL La fase org nica despu s de secarse con sulfato magn sico se concentra y cristaliza el ferroceno como cristales de color naranja Se pueden recristalizar en hexano 6 B Preparaci n de acetilferroceno A una mezcla de 10 mL de anh drido ac tico y 3 g de ferroceno contenida en un matraz provist
6. the results of the C and O experiments suggest that the former is a pure CO stretching and the latter is a pure CC stretching A further theoretical study is needed to solve this discrepancy The M O stretching vibrations of acetylacetonato complexes are most important since they provide direct information about the strength of the M O bonds Thus far they have been assigned from normal coordinate analyses 9 613 without experimental evidence As stated in Sec H 9 the metal isotope technique provides a unigue method to detect the metal ligand vibrations Nakamoto et al therefore applied this technique to acetylacetonato complexes of Fe II Crib Pd ID Cui and Ni D Their results indicate that previous band assignments on the M O stretching vibrations are essentially correct As an example Table III 49b gives the observed frequencies isotopic shifts and band assignments for Cr acac Figure 111 33b shows an actual tracing of the infrared spectra of Cr acac and its Cr analog Two bands at 463 and 358 cm of the former must be assigned to the Cr O stretching modes since they give large shifts relative to others On the other hand Pinchas et al assigned the 592 cm band to a pure Cr O stretching since it gives the largest isotopic shift 19 em by the 0 0O substitution of Cr acac However this band is shifted by only 0 7 cm by the Cr Cr substitution and
7. to 300 K in order to identify the compensation temperature Toomp 289 K Volume 71 Number 8 August1994 701 28 V2GdFes012 Magnetization per gram 100 150 Temp K 200 250 300 Figure 10 The temperature dependence of the magnetization per gram for Y Gd Fes0 2 The inset contains an enlargement of the region from 50 to 90 K in order to identify the compensation temperature Toomp 69 K room temperature This can be verified qualitatively by the observation that the Gd Fe 012 pellet is not attracted to the cow magnet at room temperature However if this pellet is cooled in dry ice or liquid nitrogen for example the pellet becomes strongly magnetic and can be picked up with the cow magnet The corresponding plot of magneti zation versus temperature for this material is shown in Figure 9 Note that at the compensation temperature 289 K and at room temperature the magnetization is very small but it increases dramatically as the temperature is lowered Also note that at low temperatures the magneti zation of Gd Fe5O1g is roughly three times larger than the magnetization af Y Fe O1 as is predicted from the de scribed simple calculation of the number of unpaired elec trons This unusual magnetic behavior suggests an interesting experi ment f a magnet is secured at the proper distance above a cooling bath upon cooling the pellet will automatically jump up to the mag net As the pellet warms it should f
8. A well known example is nitro and nitrito pentammine Co II chloride discussed in Sec III 2 A pair of true linkage isomers is difficult to obtain since in general one form is much more stable than the other As will be shown later several pairs of new linkage isomers have been isolated and infrared spectroscopy has proved to be very useful in distinguishing them 1 Thiocyanato SCN Complexes The SCN group may coordinate to a metal through the nitrogen or the sulfur or both M NCS M_ In general Class A metals first transition series such as Cr Mn Fe Co Ni Cu and Zn form the M N bonds whereas Class B metals second half of the second and third transition series such as Rh Pd Ag Cd Ir Pt Au and Hg form the M S Bonds How ever other factors such as the oxidation state of the metal the nature of other ligands in a complex and steric consideration also influence the mode of coordination Mitchell and Williams have shown that the CN stretching frequencies are generally lower in the M NCS complexes than in the M SCN complexes The C S stretching frequency is more useful in dis tinguishingthesetwoisomers 780 860cm forthe M NCSand 690 720cm for the M SCN group 3 125 The NCS bending frequency is also different between two isomers 450 490 cm for the M NCS and 400 440 cm often accompanied by weaker bands at higher frequency side for the M SCN group 195 Table III 24 lists so
9. Because the two commonest forms of coordinated NO have the same effective symmetry hence the same number of ir active vibrational modes criteria for distin guishing between them must be based on the positions of the bands rather than their number In practice the situation is quite complex and there are no entirely straightforward criteria This is because the array of frequencies depends on both the geometry and strength of coordination 14C Orvig et al Inorg Chem 1995 34 4921 P N V P Kumar and D S Marynick Inorg Chem 1993 32 1857 R Han and G Parkin J Am Chem Soc 1991 113 9707 O Yamauchi et al Inorg Chem 1996 35 7148 10 sec 111 6 COORDINATION COMPOUNDS 187 1 6 THIOCYANATO AND OTHER PSEUDOHALOGENO COMPLEXES The CN OCN SCN SeCN CNO and Ny ions are called pseudo halide ions since they resemble halide ions in their chemical properties These ions may coordinate to a metal through either one of the end atoms As a result the following linkage isomers are possible M CN cyano complex M NC isocyano complex M OCN cyanato complex M NCO isocyanato complex M SCN thiocyanato complex M NCS isothiocyanato complex M SeCN selenocyanato complex M NCSe isoselenocyanato complex M CNO fulminato complex M ONC isofulminato complex Two compounds are called true linkage isomers if they have exactly the same composition and different linkages mentioned above
10. II n Pr n Propyl 13 3 PREPARACI N DE ACETILACETONATOS DE METALES DE TRANSICI N Los acetilacetonatos forman con los elementos met licos una importante clase de complejos El ligando acetilacetonato forma un quelato muy estable capaz de coordinarse a pr cticamente todos los tomos met licos de la tabla per dica A continuaci n se propone la s ntesis de cuatro de esos complejos que responden a la f rmula general M acac 3 octa dricos cuyas diferentes propiedades se deben nicamente al diferente centro met lico 3 A S ntesis de Co acac 3 Add approximately 1 0 g of powdered Co II carbonate into a 50 mL Erlenmeyer flask and add 8 mL of acetylacetone Drop in a small magnetic stir bar and cover with a small watch glass Place the reaction vessel into a water bath on a stirring hot plate Note do not set the flask directly on the bottom of the water bath instead clamp it so that the flask is suspended within the water bath with its contents below the water line refill the bath as needed as the water evaporates during heating Stir the reaction using the magnetic stirring bar and heat the reaction to about 80 C maintaining it at this temperature for approximately 5 minutes Slowly add 6 mL of 10 hydrogen peroxide H202 drop wise at a rate of 1 2 mL min using a disposable pipette while continuing to stir the reaction mixture CAUTION 10 H20 will damage the surface of the skin Wear gloves or be extra careful
11. MoO acac acac 2 4 pentanedionate is une of the most important starting materials for preparing other di oxomolybdenum compounds of current interest 1 be cause a acac can be displaced From the coordination sphere of molybdenum by numerous ligands a acacH is volatile acacH is soluble in many organic solvents and can be removed Irom the product MoOglacac works well in fundamental IR and IH NMR experiments The synthesis described here is a modification of that re cently reported 2 The main alterations are in addition to the scale and molar ratio of reactants e starting from MoO powder which is cheaper than the con ventional NH J Mo 0 za 4420 using the common 24 13 M instead of 15 8 M NH solution a adding the reagents sequentially by weighing which facili tates the work up ending the washings with diethyl ether so that drying the product is more rapid A Typical Run In a 5 mL conical vial on an electronic balance is placed 0 25 g 1 7 mmole of MoO powder 0 40 g H2O and 0 40 g 5 5 mmole 24 NH Pasteur pipet The mixture is stirred with a glass rod for about one min to obtain a clear colorless solution exothermic reaction Then 0 75 g 7 5 mmole of 2 4 pentanedione is added and the mixture is stirred however two phases remain Finally 1 g 10 mmole of 63 HNO is added dropwise exothermic reac tion The mixture is cooled to room temperature while stirring and the soli
12. The reaction will bubble vigorously Reheat the mixture to 80 C after the addition of H202 is complete then add an additional 6 mL of H2O gt in the same manner After the second addition of H gt 0 is complete remove the water bath place the flask directly on the hotplate surface and briefly bring the flask to boiling Cool the mixture to room temperature and then place it in an ice bath for about 15 minutes or until crystallization appears to be complete Filter the product using a B chner funnel washing remnants out of the flask with deionized water 2 x 5 mL Wash with several small 2 3 mL volumes of cold ethanol make sure you chill it first or 1t will dissolve your compound Allow the compound to dry until the next lab period and then weigh the compound to get the yield of dry product 14 3 B S ntesis de Cr acac 3 Heat a water bath on a stirring hotplate Add approximately 1 30 g of CrCl3 6H20 into a 50 mL Erlenmeyer flask Drop in a small magnetic stirring bar add 20 0 mL of distilled water and stir briefly When the chromium compound has dissolved into solution add 5 0 g of urea and 4 0 mL of acetylacetone Clamp the flask in place in the water bath see note in part A and heat the water bath to a temperature greater than 90 C Heat the mixture uncovered and with vigorous stirring and deep maroon crystals will begin to form After one hour allow the reaction to cool to room temperature and then place it in an ice bath
13. The students can be given individual projects by asking them to synthesize a particular member of the Y Gd3_ Fe O12 family of compounds This might be done by giving each student the formula or x value for their target compound and informing them that 1 M solutions of Y NO3 3 Gd NO3 and FeCl are available in the lab and that everyone should use 10 mL of 1M FeCl so that ap 698 Joumal of Chemical Education 1C3HA2 D3 O12 xd D C is a dodecahedral site CN 12 lt A is an octahedral site D is a tetrahedral site CN 6 CN 4 Figure 3 The three polyhedral coordination environments that are present in the garnet structure In Gd Fes0 gadolinium ions are in the dodecahedral sites and iron atoms are in both the octahedral and the tetrahedral sites proximately the same amount of material is prepared by each student After the synthesis the students can perform the mag netic studies on their own compounds Students may be asked to design their own tests of magnetic strength to get a more quantitative measurement of the relative magneti zation of two different samples at a given temperature This might be done by measuring the distance between the magnet and the sample when an interaction is first no ticed Finally the results of the class can be tabulated to get an overall picture of the magnetic properties of these compounds Results and Discussion The magnetic properties of rare earth iron garnets have be
14. applying a linear correction derived from the Si data to the observed angles Lattice parame ters were refined from 15 18 reflections using standard least squares refinement techniques Using line positions that have not been corrected led to the same overall trend in lattice parameter with composition although there was more scatter in the data see Fig 4 Studies of Magnetic Properties To demonstrate the magnetic properties of these materi als we have used a qualitative test of the strength of the magnetism the strength of the attraction of a pellet of gar net to a cow magnet Edmund Scientific Pellets that ex hibit strong magnetism can be picked up by the cow mag net while pellets that are only weakly magnetic cannot be picked up by the cow magnet The temperature depend ence of the magnetic properties can be demonstrated by studying the magnetic behavior of the pellets of the differ ent compositions at room temperature and after cooling the pellets in dry ice or liquid nitrogen For more data points students can prepare and use other low tempera ture baths 3 More detailed investigations of the magnetism were car ried out at the University of California Berkeley with a Quantum Design SQUID magnetometer The magnetiza Volume 71 Number8 August 1994 697 24 e Gadolinium Iron O Oxygen Metal ion location within one octant of the unit cell Iron Gadolinium z 0 125 025 z 0 375 z 05 Figur
15. con 0 lt x lt 1 conocidos como bronces de wolframio cuando M es un metal alcalino donde M puede ser H Li Na K Rb Ca Sr Ba Al In Tl Sn Pb Cu Ag Cd un metal del bloque fo el cati n amonio x 2 H2 WO3 gt H WO3 La reacci n que se va a efectuar conduce a un compuesto de esta clase y supone la inserci n de hidr geno en los huecos de la estructura del s lido produci ndose formalmente la reducci n parcial de W y la oxidaci n de H a H Los electrones a adidos a la red se alojan la banda de conducci n lo que da lugar a cambio en el color del compuesto y a comportarse como conductor el ctrico Procedimiento experimental Place 500 mg of WO into a 250 mL beaker Carefully pour about 50 mL dilute hydrochloric acid 3 molar onto the WO Does anything happen Now very carefully drop some zinc filings ca 3 g into the acid After all reaction has ceased filter off the solid product After washing place it on a filter paper and observe what happens when you leave it exposed to the air Write balanced equations for both the reduction of WO and its subsequent re oxidation Make pellets of WO and H WO in a pellet press and measure the electrical resistance using an ohmmeter Is there any difference Cuestiones y experimentos adicionales 1 Escribir y ajustar todas las reacciones que tienen lugar 2 Construir con modelos la estructura del tri xido de wolframio y identificar las posiciones que pued
16. symmetry and contains eight formula units for a total of 160 atoms 5 A portion of the unit cell of GdyFes0Oy2 is drawn in Figure 2 with only the cations and selected oxygens shown for clar ity The three different polyhedral coordination environ ments for the cations in the garnet structure are drawn in Figure 3 In the case of Gd3Fe5O12 Gd occupies dodecahe dral sites and Fe occupies both octahedral and tetrahe dral sites in the structure However a wide variety of cat ions in different valence states can reside in the cation sites The primary consideration for site occupancy is ionic size This leads to many compositions that form the garnet structure Because of the similarity in ionic radii of the rare earth ions many rare earth iron garnets will form solid solution phases In the case of yttrium ionic radius 0 900 A and gadolinium ionic radius 0 938 A the complete solid so lution is stable Y Gdy FesO 2 0 x 53 Substitution of yttrium for gadolinium occurs on the do decahedral site Because Gd is slightly larger than Y we would expect that the lattice parameter a the length of the side of the cubic unit cell would increase with in creasing gadolinium content This trend is clearly seen in the data presented in Table 1 and graphically depicted in Figure 4 Many students have difficulty understanding the differ ence between a single phase solid solution compound such as Y sGd sFesO1z where th
17. 0 mL de una boca se adiciona el yoduro de arilo correspondiente 3 00 mmol cido acr lico 0 25 mL 3 60 mmol acetato de paladio entre 0 1 y 0 5 mol y una disoluci n 0 5 M de hidr xido de sodio en agua La mezcla se agita vigorosamente a temperatura ambiente con un agitador magn tico hasta que se observa la disoluci n completa de los reactivos unos 5 min Tras acoplar un refrigerante la disoluci n se refluye con agitaci n vigorosa durante 1 h Finalizado este tiempo la mezcla se deja enfriar a temperatura ambiente y se filtra para eliminar los posibles restos s lidos El filtrado se acidifica con una disoluci n acuosa 3 0 M de HCI precipitando un s lido blanco que se filtra con un embudo B chner lav ndose a continuaci n con abundante agua fr a con el fin de eliminar el cloruro de sodio y el exceso de cido acr lico que no hubiera reaccionado El s lido blanco obtenido se seca en una estufa a 100 C durante una noche y se pesa 33 cido E 3 4 acetilfenil acr lico Siguiendo el procedimiento anterior se utilizaron 0 753 g de 1 4 yodofenil etanona 0 7 mg de acetato de paladio 3 umol y 15 mL de la disoluci n de hidr xido de sodio El compuesto se obtuvo como un s lido blanco cristalino Si es necesario el producto se puede recristalizar de etanol cido E 4 2 carboxivinil benzoico Siguiendo el procedimiento anterior se utilizaron 0 759 g de cido 4 yodobenzoico 2 mg de acetato de paladio 9 umo
18. 2 Comparar los espectros vis uv de los dos complejos preparados 3 Proponer un mecanismo para la formaci n del complejo CoL Referencias E C Constable Coordination chemistry of macrocyclic compounds Oxford Chemistry Primers 1999 K Nakamoto Infrared and raman spectra of inorganic and coordination compounds 4th edition John Wiley and Sons New York 1986 A Gordon The chemist s companion A handbook of practical data techniques and references John Wiley and Sons New York 1972 53 Facile Synthesis of a Macrobicyclic Hexaamine Cobalt 11I Complex Based on Tris Ethylenediamine Gobalt 111 An Advanced Undergraduate Inorganic Laboratory Experiment Jack MacB Harrowfieid The University of Western Australia Nedlands 6009 Western Australia Geoffrey A Lawrance The Unlversity of Newcastle New South Wales 2308 Australia Alan M Sargeson The Australlan National University Canberra 2601 Australia The synthesis and resolution of tris ethylenediamine The encapsulation of the cobalt ion in the macrobicyclic cobalt III is a classical undergraduate experiment in coor ligand renders it substitution inert even in the normally labile dination chemistry which had been described in THIS cobalt II state The synthesis is a good example of reactions JOURNAL and elsewhere 1 4 Chelation of cobalt III by of coordinated ligands and it proceeds in a stepwise fashion multidentate ligands has been extended in recen
19. 4 4H20 in place of MoO3 saves time and gives a product that is not contaminated appreciably with NH4Cl A typical run is described In a 5 mL vial are placed 0 25 g 0 2 mmole of NH4 aMo7024 4H20 1 g H20 and 2 g 20 mmole 37 HCL The mixture is heated for 10 min at 100 C te g boiling water bath with stirring and the resulting solu tion is cooled to room temperature Then 0 5 g 6 4 mmale DMSO is added with stirring and the mixture is cooled again The white precipitate is filtered washed with ace tone 2 x 1 mL and peroxide free diethyl ether 2 x 1 mL and dried in air 0 37 g 75 yield of MoO2Cla DMSO is obtained as a white microcrystalline powder The compound melts at 17241 C and is very stable at ambient conditions The IR spectrum is characterized by two strong bands at 921 and 892 cm corresponding to the stretching vibrations of the cis M0O2 arrangement 3 4 Preparing OPPhs v a Catalytic Oxotransfer In a medium size test tube e g 100 x 15 mm is placed 50 mg 0 14 mmole of M002Ck DMSO 500 mg 1 9 mmole PPh and 2 5 g 32 mmole DMSO The mixture is heated at 100 C for 15 min in a well ventilated hood because the foul smelling dimethylsulfide DMS is released The resulting colorless solution is poured into a 25 mL vessel containing 12 A196 Journal of Chemical Education mL of 1 M NaOH solution this solution can be prepared by dissolving 0 5 g of NaOH in 12 mL of water The pre cipita
20. 6 Sbr oO gt 4954 SP UPDR JOSIP VU MICS jan Pir ow Mr 6 shec0 5 aa EMP WA amp S bSOt wy aby bya Wa OKOA DEA ET baby VAIS MES DEI 7 4a 2WON 4d9S 5479 Pd sud44 ap sisajuiS 1002 21 82 L0O Y YY Todos los experimentos han de codificarse con un grupo de dos o tres letras preferentemente las iniciales del alumno y numerarse consecutivamente Ejemplo el alumno Arturo Arellano lvarez usar a como c digo para su primer experimento AAA 01 Este c digo debe utilizarse para rotular los distintos documentos asociados al experimento espectros an lisis etc Ha de figurar tambi n en las etiquetas de todos los productos obtenidos A continuaci n se debe escribir el nombre del experimento que debe reflejar el prop sito del mismo Si es una s ntesis qu producto se sintetiza si un experimento de otra naturaleza en qu consiste o qu se pretende demostrar o comprobar Las reacciones qu micas deben escribirse de forma que quien lea el cuaderno tenga una visi n inmediata de lo que se ha hecho cantidades y proporci n relativa de reactivos y condiciones de reacci n Para ello se debe escribir la reacci n qu mica ajustada y sobre la flecha las condiciones de reacci n disolvente temperatura si no es temperatura ambiente Bajo cada reactivo de debe escribir su peso molecular o de la unidad f rmula y si se trata de una disoluci n su concentraci n molar y el disolvente en que est preparada En una terc
21. 8 19 19 20 21 22 23 de las reacciones en los correspondientes recipientes dispuestos a tal efecto en el laboratorio Para ello ha de seguir las instrucciones del profesor y evitar mezclar productos Manipulaci n de material y operaciones en el laboratorio El puesto de trabajo debe mantenerse en todo momento limpio y ordenado Finalizada la sesi n pr ctica se proceder al lavado de todo el material y a la limpieza de la mesa y o la vitrina Est prohibido acumular o almacenar en las vitrinas de trabajo reactivos o disolventes de cualquier tipo Todas las operaciones que comporten el uso de disolventes nocivos o desprendimiento de gases t xicos inflamables o simplemente con mal olor deben realizarse en el interior de una vitrina Despu s del montaje de un aparato de reacci n debe comprobarse que sus uniones est n perfectamente ajustadas En caso contrario podr a producirse la emisi n de gases o vapores t xicos O inflamables con el riesgo de accidentes que ello comportar a El trasvase de l quidos con pipetas no debe realizarse nunca por succi n directa sino con la correspondiente pera o goma de succi n a fin de evitar cualquier ingesti n accidental del l quido y el riesgo que ello llevar a consigo Debe evitarse el contacto de las manos con objetos calientes y la proximidad de la ropa a mecheros encendidos en caso contrario pueden producirse quemaduras incluso graves Las substancias inflama
22. H 1 M El precipitado se filtra se lava con agua 3 x 2 mL y se seca bien por succi n 35 Se procede de forma similar a la indicada en el apartado anterior utilizando como catalizador MoO acac Cuestiones y experimentos adicionales 1 Indicar la ecuaci n del proceso que conduce a la obtenci n de los dos complejos met licos y calcular los rendimientos obtenidos 2 Registrar un IR de cada uno de los s lidos obtenidos y asignar las absorciones v Mo 0 y v P 0 Bas ndose en los datos de IR discutir la oxidaci n de trifenilfosfina en funci n del catalizador utilizado 3 Discutir la informaci n que puede obtenerse por IR y IH RMN para elucidar la estructura de los complejos de molibdeno preparados 4 Por qu se utiliza una disoluci n de NaOH en los ensayos de la oxidaci n catal tica Podr a utilizarse s lo agua Bibliograf a ver p ginas siguientes F J Arnaiz y R Aguado J Chem Ed 1995 A7 A8 asi como las p ginas extraidas del texto de K Nakamoto Infrared and raman spectra of inorganic and coordination compounds 4th edition John Wiley and Sons New York 1986 36 the microscale laboratory edited by ARDEN P ZIPP SUNY Cortland Cortland NY 13045 The Conversion of Triphenylphosphine to the Oxide A Simple Experiment to illustrate Catatytic Oxotransfer Francisco J Arn lz and Rafael Aguado Laboratorio de Quimica Inorg nica Universidad de Burgos 08001 Burgos Spain Ox
23. M Compound v CN v CSy NCS K NCS 2053 748 486 471 Eta N Cr NCS 6 2078 z 483 Et4N 2 Co NCS 4 2065 oN 481 838 EtaN a Ni NCS 2112 828 470 2103 Et4N 2 Zn NCS 2072 837 482 Et4N 2 Pd SCN 2112 698 465 433 2109 694 429 418 Et N Au SCN 4 2127 695 454 415 Et4N 2 Pt SCN 6 2120 692 461 457 418 415 Et C Hs gt The S bonded complex may exhibit a band at 880 810 cm which is the first overtone of NCS Care must be taken therefore in distinguishing this band from v CS 0 12 SEC III 6 COORDINATION COMPOUNDS 189 which L is a phosphine an arsine a stibine or a phosphite Infrared spectra show that all these Rh I complexes are N bonded The cis and trans isomers of Co III NCS complexes can be distinguished from infrared spectra 9 292 As stated before the distinction of true linkage isomers by infrared spec troscopy has been made for Co NH3 s NO or ONO JCI and KFeCr CN 8 Basolo et al succeeded in isolating true linkage isomers of trans PA As Ph 3 NCS gt The bright yellow N bonded complex absorbs at 2089 CN stretching and 854 cm CS stretching the yellow orange S bonded complex absorbs at 2119 cm CN stretching although the phenyl absorption near 700 cm obscures its C S stretching band Infrared spectra of link age isomers have also been reported for Pd bipy NCS SCN 1 9 295 and Pd As n C H 3 NC
24. QU MICA EXPERIMENTAL III PROGRAMA DE QU MICA INORG NICA gt Q O m P gina Presentaci n 1 El cuaderno de la asignatura 3 2 Preparaci n y caracterizaci n de complejos de N quel 8 3 Preparacion de acetilacetonatos de metales de transicion 14 4 Experimentos en qu mica del estado s lido Preparaci n de granate Yx Gd3 xFes012 20 Inserci n de hidr geno en tri xido de wolframio 31 5 Cat lisis homog nea La arilaci n del cido acr lico mediante la reacci n de Heck 33 de molibdeno VI 6 40 preparaci n de ferroceno y acetilferroceno 7 Efecto plantilla 46 S ntesis de un complejo encapsulado de cobalto 51 AP NDICE 1 SEGURIDAD EN EL LABORATORIO 56 Presentaci n En este cuadernillo de pr cticas se resume la informaci n necesaria para la realizaci n de los experimentos de Qu mica Inorg nica de la asignatura Qu mica Experimental III Los objetivos de esta parte de la asignatura son Conocer las t cnicas y m todos de s ntesis y caracterizaci n de compuestos inorg nicos con especial nfasis en compuestos de coordinaci n y organomet licos y ser capaces de llevarlas a cabo Asignar y determinar la estructura de los distintos tipos de compuestos inorg nicos utilizando las t cnicas instrumentales de caracterizaci n adecuadas Predecir y analizar las propiedades de los compuestos inorg nicos Interpretar los datos procedentes de las reacciones q
25. S SCN gt A complex of the composition Cu tren NCS tren triaminotriethylamine exhibits two CN stretching 2094 and 2060 cm and two CS stretching 818 and 745 cm bands Based on this and other data Raymond and Basolo suggested that this complex may contain both Cu NCS and Cu SCN linkages Later Jain and Lingafelter have shown from x ray analysis that one NCS group is bonded to the metal through nitrogen and the other group is not coor dinated with it Bertini and Sabatini suggest that Pd 4 4 dimethyl bipy NCS may contain both types of coordination since it exhibits two CN stretch ings at 2120 and 2090 cm The NCS group also forms a bridge between two metal atoms The CN stretching frequency of a bridging group is generally higher than that of a terminal group For example HgCo NCS Co NCS Hg absorbs at 2137 cm whereas Et N Co NCS absorbs at 2065 em According to Chatt and Duncanson the CN stretching frequencies of Pt IT com plexes are 2182 2150 cm for the bridging and 2120 2100 cm for the terminal NCS group P r Pr Pt SCN CI compound T exhibits one bridging CN stretching whereas P 7 Pr 3 Pt SCN compound ID exhibits both bridging and terminal CN stretching bands Thus the infrared spectra suggest the structure of each compound to be N N C C n Pr 3P S CI n Pr P SS ASON Ci s P n Pr NCS 5 P n Pr 3 C C N N I
26. a AAA 01 opcional Vombre del experimento Ecuaci n qu mica ajustada condiciones de reacci n Peso molecular o peso de la unidad f rmula de los reactivos Valores de las magnitudes experimentales medidas Moles Descripci n del experimento Cantidad obtenida rendimiento En la hoja siguiente se da un ejemplo ey tge Ww L y DY ZK b LR hosi Skya eresi yg Bores oy ye Ww PEN ONWY Sa WERD FP EKO O E Cua t J EP bel G WOE KG Peg EFIE Kg PESE LAIC NWY Da WERD ENS ME ya YOR ey EEDE NWY fh PUT vunppiedwe2 v opoizcbey TI PP Tw FO ue bw 9 008 Xyy NWY CD DELE DEEE N upiSue2 BP VYOZ Ote pay odolny we YT il ZEE AOM 00D Obi yy LOGIA VE A DLL DUORZEDY W257 IOI ow b bir EON vg 0723478 W p OE Josip Ti se ws bw Or DUO UD Opipel POPAZDTPUOT SUI NV bre fx M DI EA AA o DEL M OOE fa CEER D pd A8 SSM RD Ood OPO I7DPD OPJ SISUDUY ZSE opwenepuey E bet varango ag WAO O 00 e2serndwop je VZY PISNO UPIDON OSIP OJ AD OROJOS je UD IDLQUEDUOD JH PA EER A 9 97 2541 ORO CHpISH UN OPAOSAY TfR Bp pw OS wa Ojopupi NOS P PZYOPSMOA BS o2pssrdwop PTO PPE YA A yw SXE O 77 UOD opin VDOJE UD PALA PS ye Sl o 27 PPOLO PS fu S BP UBICA UN D2SVI OSODA D BALBAJOSIP je PHU YP OD UPIIDODA V UD OPD4O p ighy 2 Mayo veod 35 81y us ie up ag A OAY vum P STETS gt Upro BO UOD ONO ag ott P1 E pgs DC Yarsyals DIED PPO PS je St O HZHO29 O US omy dead
27. ad molar Datos de espectroscopia uv vis Disolvente y concentraci n de la muestra Longitud de onda y intensidad de las bandas de absorci n Datos de espectroscopia IR Disolvente o agente dispersante utilizado N mero de onda de las absorciones m s significativas Datos de espectroscopia RMN Disolvente y concentraci n aproximada de la muestra Temperatura a la que se ha adquirido el espectro Equipo en el que se ha registrado la muestra y n cleos registrados Para cada espectro desplazamiento qu mico multiplicidad y intensidad integrada de todas las se ales y valor de las constantes de acoplamiento Datos anal ticos Ensayos anal ticos realizados cuantitativos y cualitativos y su resultado Normas de seguridad Ver la normativa y los consejos del Servicio de Prevenci n de Riesgos Laborales de la UVa http www uva es opencms contenidos serviciosAdministrativos recursosHumanos pre vencionRiesgosLaborales consejosPreventivos Enlaces_Listados_Quimicos Borrador_n ormas_usuario Bibliograf a Al final de cada pr ctica se se ala la bibliograf a que se debe consultar Otras fuentes de inter s Dodd R E y Robinson P L Qu mica Inorg nica Experimental Revert 1981 Schlessinger G G Preparaci n de Compuestos Inorg nicos en el Laboratorio Ed Continental 1986 Szafran Z Pike R M Singh M M Microscale Inorganic Chemistry A Comprehensive Laboratory Experience W
28. ada por un lcali lave r pidamente las zonas afectadas con una soluci n saturada de cido b rico o una soluci n al 1 de cido ac tico y posteriormente con abundante agua 60 3 Quemaduras por calor Enfriar la zona afectada con agua abundante Aplicar la pomada id nea que encontrar en el botiqu n del laboratorio 4 Cortes Si son peque os la herida se lavar con agua se desinfectar alcohol O agua oxigenada y se cubrir con gasa Si el corte es grande o profundo puede precisar de asistencia m dica Informar de ello al profesor que adoptar las medidas pertinentes 5 Incendio del vestido Si alg n l quido inflamable se proyecta ardiendo sobre la bata las llamas han de extinguirse mediante la oportuna ducha o cubriendo las llamas con una manta bata o ropa de algod n Avisar al profesor y en su caso desvestirse y examinar las quemaduras si son leves proceder como en 3 si revisten importancia es necesaria la atenci n m dica 61
29. ada una de las s ntesis realizadas y calcular los rendimientos de los productos sintetizados 2 Determinar el Ay de los compuestos sintetizados a partir de sus espectros visible ultravioleta 3 Hacer un espectro IR de los compuestos preparados y compararlos con el de la 2 4 pentanodiona Las bandas de tension C C y C O aparecen entre 1500 y 1700 cm 4 Discutir las principales diferencias y semejanzas de los procedimientos de s ntesis Para que la 2 4 pentanodiona se coordine como acetilacetonato es necesario que se deprotone Indicar qu especie qu mica ac a como base en cada una de las reacciones Bibliograf a 1 Bryant B E Fernelius W C Inorg Synth 1957 5 188 2 Charles R G Pawlikowski M A J Phys Chem 1958 62 440 3 Fernelius W C Blanch J E Inorg Synth 1957 5 130 4 Charles R G Inorg Synth 1963 7 183 Ver tambi n paginas siguientes Extraidas del texto de K Nakamoto Infrared and raman spectra of inorganic and coordination compounds 4th edition John Wiley and Sons New York 1986 III 21 COMPLEXES OF B DIKETONES 1 Complexes of Acetylacetone A number of diketones form metal chelate rings of type A Ru R C R h se 7 Type A Oy o Among them acetylacetone acacH is most common R Ry CH and Ru H According to x ray analysis on Fe acac the chelate ring is planar and symmetrical C symmetry and the tw C O bonds are equivalent a
30. all back into the cooling bath where upon cooting again the pellet will repeat this motion cycle This behavior should continue indefinitely provided that the cooling bath is teplenished periodically and provided that the pellet does not fall out of the range of the magnet Bin this particular measurement the magnetization is not exactly zero probably due to the presence of a small amount of GdFeQ in the sample 702 Joumal of Chemical Education The effect of combining both yttrium and gadolinium in the garnet structure in the solid solution compounds is that the compensation temperature becomes a strong func tion of composition 6 This is obvious from the magneti Table 2 Variation in Compensation Temperature Teomp With Composition for Y Gd3 xFes012 Composition Tcomp K Reference YgFesOr2 ME This work Y2 7Gdo3Fe5012 6 only measured abova 73 K Y2 1Gdo gFe5O12 3 6 only measured above 73 K Y2Gd1Fe5O12 69 This work Y1 8Gd1 2Fe5O12 93 6 Y1 2Gdi sFesO12 158 6 Y Gd2FesO12 175 This work Yo eGd2 4FesO12 218 6 GdsFesO12 289 This work No compensation temperature was observed down to 5 K 29 60 0 50 0 40 0 30 0 20 0 Magnetization per gram 10 0 0 0 0 50 100 YGd2Fe5012 175 Temp K 150 200 250 300 Temp K Figure 11 The temperature dependence of the magnetization per gram for Y Gd gt Fe5O42 The inset contains an enlargement of the region from 130 to 220 K in order to id
31. and 3 mL of 0 3 M Y NO solution Add 5 10 mL of 2 M NaOH dropwise to the metal ion solution in order to precipitate a reddish brown solid Decant the solution and wash the remaining solid repeatedly with water until the wash is no longer basic test with pH paper Filter and dry the solid in a drying oven 120 C overnight Press the powder into 1 2 inch diameter pellets using a standard pellet press and fire in a furnace at 900 C for 18 24 hours A visible color change from reddish brown to olive green after firing indicates that a reaction has taken place Determine the strength of the attraction of your pellet of garnet to a strong magnet at room temperature dry ice temperature and liquid nitrogen temperature Discuss your procedure with other students in the class and agree on a method that will allow comparison of the magnetic effects as a function of the garnet composition Cuestiones 1 Identificar en el granate sintetizado los iones M M y M que ocupan posiciones dodeca dricas octa dricas y tetra dricas respectivamente 3 Indicar las cantidades que ha empleado de cada reactivo y qu composici n de granate se obtiene con ellas 2 Explicar a partir de las variaciones en composici n la variaci n en el magnetismo observado cualitativamente para cada una de las cuatro muestras de su grupo de trabajo Bibliograf a A F Wells Qu mica Inorg nica Estructural Ed Revert Barcelona 1978 W D Calister
32. as a los experimentos y responder a las cuestiones y problemas asociados a cada pr ctica En el cuaderno de la asignatura no se deben incluir los c lculos matem ticos elementales ni se debe usar como papel en sucio Notas previas a los experimentos La realizaci n de un experimento qu mico requiere cierta preparaci n previa Antes de hacerlo se debe tener una m nima idea de las propiedades qu micas de los reactivos y productos de la reacci n Para ello lo m s recomendable es acudir a los libros de Qu mica Inorg nica b sica pueden ser el de Greenwood y Earnshaw Chemistry of the Elements el de Holleman y Wiberg Inorganic Chemistry o cualquier otro de qu mica descriptiva y leer las propiedades generales del elemento principal del experimento En particular la estabilidad de los distintos estados de oxidaci n reactividad y propiedades cido base Eso permitir entender el resultado del experimento y prever sus dificultades Adem s antes de realizar el experimento es necesario preparar el material necesario y los reactivos y evaluar los posibles riesgos que conlleva Tambi n si es necesario hay que calcular las cantidades necesarias de reactivos y disolventes a usar manteniendo las proporciones molares del gui n En las hojas reservadas para las cuestiones y problemas se deben resumir las notas previas a cada experimento Listado de material y reactivos necesario Comprobar su disponibilidad y estado Posi
33. as indicaciones b sicas para la interpretaci n de los resultados Manipular un equipo sin saber exactamente lo que se est haciendo no tiene ninguna justificaci n Si no sabes usar una aparato pregunta a tu profesor antes de hacer nada Como parte de tu formaci n debes habituarte a identificar los riesgos inherentes a la manipulaci n de productos qu micos y a actuar en consecuencia No se trata solo de cumplir con las normas de seguridad b sicas sino de ser capaz de hacer una previsi n de riesgos y medidas de precauci n que es necesario adoptar Tambi n te debes habituar a elaborar un cuaderno de laboratorio inteligible detallado y ordenado En las p ginas siguientes se te dan instrucciones para ambas cosas que deben quedar recogidas en el cuaderno de la asignatura Finalmente recuerda que la asignatura est constituida por dos partes a El trabajo experimental que se desarrolla en el laboratorio b La preparaci n de la pr ctica y el estudio de los temas relacionados que se desarrolla fuera del laboratorio La superaci n de los cr ditos de la asignatura requiere el aprovechamiento de ambas 1 EL CUADERNO DE LA ASIGNATURA La realizaci n de la asignatura lleva aparejada la elaboraci n de un cuaderno con las siguientes caracter sticas a Debe estar formado por hojas inseparables b Un grupo de hojas contiguas se reservar n como cuaderno de laboratorio Otro grupo se reservar para escribir las notas previ
34. bles nunca se deben calentar a la llama directa sino usando un calefactor el ctrico o una manta calefactora Ha de disponerse adem s el correspondiente dispositivo de recogida o condensaci n de vapores No se debe calentar un sistema cerrado pues el aumento de presi n por evaporaci n del disolvente puede producir una explosi n Los vapores emitidos por las sustancias no deben olerse directamente Si es necesario comprobar su olor basta acercar el rostro a 10 20 cm del recipiente y pasar la mano sobre l en direcci n a las fosas nasales los vapores as arrastrados llegan f cilmente a la nariz La mayor a de los cortes en el laboratorio se producen en el manejo de tubos de vidrio cortado introducci n en tapones etc por lo que ste debe realizarse 58 siempre con el auxilio de una bayeta 24 Antes de abandonar el lugar de trabajo se debe comprobar que las llaves de gases y los grifos de agua est n cerrados y que se encuentran desconectados todos los aparatos el ctricos utilizados en la pr ctica Mientras se trabaje o se permanezca en los laboratorios queda prohibido maquillarse fumar ingerir bebidas o alimentos y usar material de laboratorio para comer o beber 59 PROCEDIMIENTO PARA CASOS DE EMERGENCIA Y O ACCIDENTES 1 PROTEGER Haga el lugar seguro para usted y el accidentado eliminando cualquier riesgo 2 AVISAR Comunique la urgencia inmediatamente Al profesor responsable del laboratorio Si no
35. bles riesgos y precauciones que es necesario adoptar Se debe indicar si las reacciones son fuertemente exot rmicas o si se produce desprendimiento de gases Tambi n si en alguna de las manipulaciones hay riesgo de incendio explosi n inundaci n rotura de vidrio etc as como si alguno de los reactivos o disolventes es particularmente t xico o nocivo por cualquier raz n y las medidas de precauci n que se deben tomar para su manipulaci n Se puede encontrar informaci n acerca de las caracter sticas de cada compuesto en la p gina de cualquier suministrador de productos qu micos as como en la p gina del Ministerio de Empleo y Seguridad Social http www insht es portal site Insht menuitem a82abc159115c8090128ca10060961ca vgnextoid 4458908b51593110VgnVCM100000dcOcascORCRD Cuestiones y problemas Una vez realizado el experimento se escribir n a continuaci n de las notas previas las respuestas a las cuestiones y problemas que aparecen al final de cada gui n de pr cticas Cuaderno de laboratorio En las hojas reservadas como cuaderno de laboratorio se escribir n los experimentos realizados de acuerdo con el siguiente esquema general Cada s ntesis de laboratorio se escribe en una hoja par del cuaderno y los datos experimentales de caracterizaci n en la hoja impar siguiente de forma que al abrir el cuaderno se pueda ver toda la informaci n relativa a ese compuesto C digo del experimento Fech
36. bstituted species Table 11 50 lists the observed 19 4 EXPERIMENTOS EN QU MICA DEL ESTADO S LIDO 4 A Preparaci n del granate Y Gd Fe O Los granates son minerales de f rmula general M M S10 M y M pueden ser el mismo elemento Por extensi n se denomina granate a aquellos s lidos de f rmula general M M M O y que tienen la misma estructura Octaedros M O y tetraedros M O formando una red en la que cada octaedro est unido por cada v rtice a un tetraedro y viceversa En esa red los cationes M ocupan posiciones dodeca dricas n mero de coordinaci n 8 El granate que se va a preparar contiene dos tipos de cationes M Y II y Gd III que forman una disoluci n s lida de tal forma que ambos metales pueden sustituirse en la red cristalina para dar cualquier composici n intermedia 0 lt x lt 3 El resto de los cationes son Fe III algunos de los cuales tienen un entorno octa drico M y otros tetra drico M Una de las propiedades interesantes de los granates es que son materiales magn ticos En este caso el comportamiento es ferrimagn tico y se deriva de la presencia de tomos de gadolino HI IC 8 Xe 4f 7 electrones desemparejados y hierro III en los entornos de coordinaci n del granate IC 6 o IC 4 Ar 3d tiene 5 electrones desemparejados El Y III tiene configuraci n electr nica de gas noble Kr por lo que no contribuye al magnetismo de la muestra Lo
37. cannot be assigned to a pure Cr O stretching mode It may be due to a ligand vibration in which the oxygen atom moves appreciably e g CO out of plane bending It 18 sec 11 21 COORDINATION COMPOUNDS 249 TABLE III 49a OBSERVED FREQUENCIES AND BAND ASSIGNMENTS OF ACETYLACETONATO COMPLEXES cm Cufacac Pd acac Fefacac z Predominant Mode 3072 3070 3062 v CH 2987 2990 2895 20 265 265 CH3 2920 2920 2920 1577 1569 1570 CO MCs O 1552 1549 combination 1529 1524 1525 CO ACC 1461 1425 1445 8 CH CC 1413 1394 1425 CH 1353 1358 1385 1274 1272 1274 W C CH C C 1189 1199 1188 S CH W C CH 1019 1022 1022 p CH 936 937 930 AC C CoO 780 786 801 gt 70 a CH 771 684 700 el v C CH ring def 667 v M O 653 678 656 T cx On o o o zi ring def M O 451 463 433 v M O v C CH 431 441 415 408 ring def 291 294 298 v M O 1 45 1 85 1 30 K M O mdyn A UBF Pure ring deformation should be noted that an isotopic substitution of the atom of the ligand atom bonded directly to a metal shifts the metal ligand as well as ligand vibrations involving the motion of the a atom Thus the metal ligand vibrations cannot be uniquely assigned by this method Behnke and Nakamoto prepared three deutero analogs of K Pt acac Cl and calculated a set of UBF force constants to fit the observed frequ encies of four isotopically su
38. cidente Manipulaci n de reactivos y residuos Antes de utilizar un producto el alumno debe leer atentamente la etiqueta advertir los riesgos espec ficos que comporta su uso y seguir en su manipulaci n las normas o consejos de seguridad que se le indiquen Los productos inflamables o explosivos deben mantenerse siempre alejados de puntos o focos calientes mecheros estufas radiadores placas y mantas calefactoras hornillos etc Una sustancia inflamable o explosiva no debe calentarse nunca a fuego directo mechero Bunsen Debe evitarse la contaminaci n de los productos o reactivos que se utilicen Para ello se extremar n las condiciones de limpieza en su manipulaci n no utilizando esp tulas vasos matraces etc que no est n perfectamente limpios Se tomar del envase original la cantidad de producto necesaria y no se devolver al mismo el exceso empleado Los productos o reactivos que puedan verterse accidentalmente sobre la mesa de trabajo deben neutralizarse antes de proceder a su eliminaci n Por ejemplo si se trata de una disoluci n de base se neutralizar con hidrogenocarbonato s dico o cido ac tico diluido si de un cido con hidr xido c lcico en polvo si de un oxidante con sulfito s dico s lido etc No debe arrojarse a las pilas o fregaderos material o producto alguno que pueda obstruir los desag es El alumno debe tener sumo cuidado en verter los residuos o productos desechados 57 16 17 1
39. ctor was at 254 nm Experlmental Conditions Since ferrocene acylates readily the reaction may be investigated ata variety of temperatures from 45 100 C A styrofoam cup seryes as an excellent individual constant temperature bath The results described here were obtained at 100 C with each student assigned a different reaction time Procedure Place 0 2 g 0 001 mole of ferrocene 1 0 ml of acetic anhydride and 0 1 ml of 85 phosphoric acid into a small test tube cork shake and immediately place in a constant temperature bath At designated intervals 15 sec 30 sec etc quench the reaction by pouring onto about 5 g of crushed ice Allow the red brown mixture to stand with occasional stirring for 15 min Filter wash the solid with 5 ml of cold Cch e CH3 Cos o s HaPOa e Fe CHC 0 gt Fe B dm pr o u iH w Figure 1 Acylation of ferrocene 380 Journal of Chemical Education t 4 SAMPLE I Ferrocene li Acatylferrocene MI 1 1 Diacetylferrocene ABSORBANCE 254 nm 1 0 AUFS 0 5 10 TIME min Figure 2 Liquid Chromatogram of the Separation of Standards of Ferrocene I Acetylferrocene ll and 1 1 Diacetylferrocens 4111 Table 1 k and R Values for Ferrocene and Some Acylated Derlvatlves Compound K Pr Ferrocene I 2 14 0 9 Acatylferrocene li 1 00 0 6 4 1 Diacetylferrocene II 0 64 0 3 Table 2 LC Analysis of Products of Acylation of Ferrocene at 100 C r Product Co
40. d formed is ground until a yellow pow der results Powdering the initially lumpy precipitate im proves the purity of the product and requires less than 5 min The product is filtered through a Hirsch funnel washed consecutively with distilled water 4 x 2 mL etha nol 2x 2 mL and peroxide free diethyl ether 2 x 2 mL and dried in air Washings alsa may he done by decanting The powder settles sufficiently in less than 1 min so that more than 75 of the liquid can be removed Using 2 Pas teur pipet is advisable in this case to reduce product losses because MoOz acac forms a supernatant skin every time water is added The entire process requires about 30 min About 0 19 p of a light yellow finely powdered product melting at 179 1 C the reported value is obtained The IR spectrum of the compound shows two strong bands at 900 and 930 cm corresponding to the stretching vibrations characteristic of the cis MoO arrangement Singlets at 2 12 and 2 14 5 CD2 Cl2 room temperature assignable to the two sets of inequivalent methyl groups see drawing are observable in the 1H NMR spectrum HC H HC Acknowledgement I am grateful to the editor for helpful comments Literature Cited 1 See e g la Srivastava A Ma Y Pankayateelvan R Dinges W Nicholas K M J Chem Soc Chem Com mun 1982 353 tb Bustos C Manzur Carrillo D Robert F Gouzerh P fnorg Chem 1994 33 1427 2 Chukravo
41. diacylated products Thin layer chro matograms were run on silica using a developing solution of tolu ene methanol in proportions of 20 1 Conclusions Monitoring the ferrocene acylation reaction by reverse phase le is an excellent method of integrating this important separations tech nique into the undergraduate organic laboratory and of providing students with hands on experience with lc Because of the short re action time simple product work up and rapid le separation many students have the opportunity to complete this experiment in one laboratory session Acknowledgment The author wishes to thank the National Science Founda tion Undergraduate Research Participation Granis GY5892 and GY7241 and Ms Gerry Granda Ms Helen Grzybowski and Ms Diane Sommerer for their work in tlc analysis Thanks are also extended to Waters Associates Milford MA for providing materials and financial support Literature Cited 1 Rosenklum M Chemistry of the Iron Group Metallocenes Ferrocene Ruthenocene and Osmocene John Wiley and Sons Inc New York 1965 2 Dauben W G Organic Reartions 17 John Wiley and Sons Inc New York 1963 3 Clark A K and Bell C E Laboratory Experience in Organic Chemistry Charles E Merrill Publishing Co Columbus Ohio 1972 p 55 4 Fieser L F and Williamson K L Organic Experiments 4th Ed D C Heath and Cu Lexington MA 1979 p 169 5 Adams
42. different local moments are present in ferrimag nets These unequal spins align antiparallel antiferro magnetically below the Curie temperature T but be cause the spins have different magnitudes the cancellation is not complete A simple schematic repre senting the differences between the magnetic ordering in ferromagnetism antiferromagnetism and ferrimagnetism is shown in Figure 7 The magnetic properties of the rare earth iron garnets can be understood by considering that each type of coordi nation site in the crystal structure leads to a separate mag netic sublattice Thus for Gd Fe O there are three mag netic sublattices comprised of the unpaired spins of the ee JETT TT u LTT LT AA Figure 7 The magnetic ordering of linear arrays of spins unpaired electrons in a ferromagnet antiferromagnet and a ferrimagnet Fer rimagnetism is the type of magnetic ordering that occurs in the rare earth iron gamets Y Fe 0 30 0 28 0 4 E 20 E E 24 0 220 50 100 180 200 250 300 Temp K Figure 8 The temperature dependence of the magnetization per gram for Y FesO 2 27 different cations the gadolinium sublattice the octahedral iron sublattice and the tetrahedral iron sublattice The to tal magnetic moment can be represented by eq 1 M T My T M T M T 1 where M 7 represents the temperature dependent mag netization of the tetrahedral sublattice M T represents the temperatu
43. domain memory storage the ability to move the do main walls underlies the writing capabilities in the read write mode 5The ordering temperature of an antiferromagnet is called the Neel temperature Ty A Paramagnet Spins are randomized by thermal energy B Ferromagnet Spins are ordered in magnetic domains C Ferromagnet H NUDU spe tre U magnetic field M Figure 6 a In the absence of an applied magnetic fieki the unpaired electrons or spins of a paramagnet are randomly oriented due to thermal energy In contrast the spins of a ferromagnet b spontane ously align with each other within regions known as magnetic do mains c In an applied magnetic field the individual magnetic domains all align with the field resulting in a large overall magnetiza tion 700 Journal of Chemical Education temperature 7 thermal energy is sufficient to break the alignment of the spins and the material exhibits simple paramagnetism But below T the aligning forces over come thermal randomization the spins are locked in align ment and the material becomes ferromagnetic Another type of magnetic ordering that can occur in sol ids is antiferromagnetism In this type of magnetic behav ior the spins align opposite to each other below the order ing temperature to lessen the overall magnetism Ferrimagnetism the type of magnetic ordering that oc curs in the garnets differs from ferrgmagnetism in that ions with
44. e 2 Portion of the unit cell of the gamet structure of Gd3Fe5012 is shown at the top All of the metal ions in one eighth of the unit cel are drawn along with the oxygen ions that complete the octahedral or tetrahedral coordination around the iron atoms The rest of the atoms have been deleted for clarity At the bottom horizontal sections per pendicular to the z direction are shown to indicate the precise posi tions of the iron and gadolinium ions within this octant of the unit cell Note that in this figure the z 0 section corresponds to the top face of the cube and z increases in the downward direction tion was measured as a function of temperature in an ap plied magnetic field of 40 kGauss Suggested Use in Lab Due to the need to fire these samples in a high tempera ture furnace for 18 24 h we would suggest that the in structor allow two to three laboratory periods for this ex periment perhaps running concurrently with another experiment One period is necessary for the preparation of the hydroxide precursor and depending on the availability of furnaces the firing can be done in the week between two meetings In the second laboratory period students can as certain whether a second firing is necessary to complete the reaction The magnetic studies then can be carried out in a second or third laboratory period If the instructor in cludes X ray powder diffraction in this experiment the time must be adjusted accordingly
45. e ocupar el hidr geno Trabajo en grupo 31 3 Calentar una peque a muestra en la estufa a unos 100 C durante unos d as anotar cualquier cambio de aspecto y explicar a qu se debe Tomar otra peque a muestra y agitarla en un tubo de ensayo con un par de mL de H O diluida Anotar y explicar los cambios observados Bibliograf a A F Wells Qu mica Inorg nica Estructural Ed Revert Barcelona 1978 E Kikuchi N Hirota A Fujishima K Itoh M Murabayashi J Electr Chem 1995 381 15 19 DOI http dx doi org 10 1016 0022 0728 94 03649 N 32 5 CAT LISIS HOMOG NEA 5 A La arilaci n del cido acr lico La reacci n de Heck conocida tambi n como Mizoroki Heck es un m todo eficiente y muy usado para la formaci n de enlaces carbono carbono en el que un alqueno y usualmente un haluro de arilo o vinilo se acoplan en presencia de un catalizador de paladio Esquema 1 La reacci n es frecuentemente regio y estereoselectiva form ndose predominantemente el alqueno trans La adici n de una base es necesaria para eliminar el haluro de hidr geno formado Pa B Ar X B H X Ar Esquema 1 Cuando se usa un disolvente org nico se suele emplear trietilamina como base pero si los reactivos son solubles en agua se puede sustituir la trietilamina por bases m s comunes como hidr xido o carbonato de sodio Procedimiento experimental En un matraz de fondo redondo de 5
46. ea Se transfiere la disoluci n y la varilla imantada a un vaso de 250 mL filtrando si permanece alg n s lido sin disolver y se lleva a ebullici n durante diez minutos con agitaci n El volumen final debe ser ligeramente inferior a 50 mL Se retira la varilla imantada y se deja enfriar la disoluc n primero hasta temperatura ambiente y luego en un ba o de hielo y sal durante media hora Durante este tiempo el compuesto cristaliza en peque as agujas de color salm n El s lido se filtra en placa Se retiran las aguas madres concentr ndolas se puede obtener m s compuesto se lava el s lido con etanol 2 veces con 5 mL y se seca pasando aire Concentrando las aguas madres se puede obtener una segunda fracci n cristalina cuidado si se concentra demasiado cristaliza NaCl con el producto Se obtienen unos seis gramos de producto 2 Synthesis of cobalt complex of encapsulating ligand Ly Procedure Dissolve 2 45 g of Co en 3 Cl3 and 1 2 g of Na CO in 25 cm water and add 18 cm of 40 aqueous formaldehyde with CAUTION and 2 5 cm of nitromethane Allow the mixture to stand at room temperature for 4 hours and add 5 cm ethanol to induce crystallization Filter the resulting solid off using suction and wash it with ethanol 10 cm and diethyl ether 10 cm Dry the solid in air and store it Cuestiones 1 Explicar brevemente los factores que contribuyen a la estabilidad de los complejos con ligandos macrociclo
47. en of great interest for the past two decades Rare earth iron garnets R Fes0 gt can be prepared with all of the rare earth ions except R La Ce Pr or Nd Detailed reviews of the crystal chemistry and the physical properties of rare earth iron garnets abound in the literature 4 Structure Gadolinium iron garnet GIG and yttrium iron garnet YIG are members of the garnet structural family of com plex oxides The general formula for a garnet is Cai A210D3JO12 where the C cations occupy dodecahedral sites the A cations occupy octahedral sites and the D cat Table 1 Variation in Cubic Lattice Parameter a with Composition for YxGds xFes012 Composition Lattice Parameter A Y3FesO12 12 370 1 Y2 5Gdo 5FesO12 12 382 2 YaGd FesO12 12 402 2 Y1 5Gd1 5FesO12 12 423 2 Y Gd2FesO12 12 437 2 Yo5Gd25Fes012 12 450 1 Gd3FesO12 12 468 2 25 Lattice parameter A 6 8 12 38 12 36 12 34 0 0 0 5 1 0 1 5 2 0 2 5 3 0 xin Gds Fe 0 5 Figure 4 The variation in the cubic lattice parameter a with compo sition in Y Gd3 FesO 2 The corrected data were obtained by adding silicon as an intemal standard prior to collecting the diffraction data The line positions of Y Gdg FesO were corrected for systematic errors by applying a linear correction derived from the Si data to the observad angles ions occupy tetrahedral sites in the crystal structure The unit cell of the garnet structure has cubic
48. entify the compensation temperature Toomp 175 K zation behavior plotted in Figures 10 and 11 for the two intermediate compositions Y Gd Fe s0O 2 and Y GdzFe 0 12 From the data it is clear that the compensation point for Y Gd FesO is 70 K Fig 10 and for Y Gd2FesQy2 is 175 K Fig 11 Again these can be verified qualitatively with the cow magnet If Y Gd Fes0Oyz is cooled in liquid nitrogen the pellet cannot be picked up with the cow magnet Like wise if Y GdzFes0y2 is cooled in dry ice the pellet only weakly responds to the cow magnet This information is summarized in Table 2 which lists the compensation tem peratures for various compositions in the solid solution se ries Y Gd Fe5O12 Conclusions This laboratory presents an opportunity to introduce solid state chemistry into the introductory chemistry course The synthesis and qualitative magnetic measure ments described above are not difficult yet they provide insight into preparative chemistry and the magnetic prop erties of solids In addition the experiment is such that the students have their own individual compound to prepare in order to contribute to the overall understanding of the system We believe that this team approach generates a more positive laboratory experience Acknowledgment The authors would like to thank Frank DiSalvo at Cor nell University for providing the inital suggestion for this experiment Debbie Stafslien for early
49. era l nea hay que especificar la cantidad que se ha empleado en las unidades en que se ha medido si es un s lido su peso si un l quido o una disoluci n su volumen En la cuarta l nea se debe escribir la cantidad en moles a la que corresponde la cantidad medida de cada reactivo de esta forma se puede comprobar inmediatamente si los reactivos est n o no en proporciones estequiom tricas La descripci n del experimento debe incluir la descripci n detallada de todas las Operaciones que se efect an para llevar a cabo el experimento Esta parte probablemente ser muy semejante a la que aparece en el gui n de la pr ctica No se trata de ser creativo sino de adquirir el h bito de redactar correctamente los procedimientos experimentales para poder hacerlo cuando no exista gui n de apoyo Adem s de la descripci n de la s ntesis o del experimento ha de incluirse cualquier incidente variaci n o modificaci n del gui n as como cualquier observaci n experimental adicional A continuaci n se debe indicar el resultado del experimento si se trata de una s ntesis el peso y el rendimiento expresado en tanto por ciento En la hoja siguiente normalmente la hoja impar se deben incluir los datos espectrosc picos y anal ticos asociados a la muestra Datos de conductividad disolvente empleado temperatura concentraci n de la muestra utilizada conductividad espec fica medida de la disoluci n y del disolvente puro y conductivid
50. ere is a 50 probability that the atom on the rare earth site is Y or Gd and a physical two phase mixture containing equal amounts of Y Fes0O 12 and Gd Fes0Oy2 The X ray powder patterns illustrate beau tifully the difference between these two cases Because the The shifts in the positions of the lines in the X ray powder diffrac tion pattern are not clearly visible to the eye However by accurately determining the position of the lines and refining the lattice parameter the shifts in the lattice parameters are significant Theoretically ferromagnetism is feasible in a liquid although a lig uid ferromagnet has not to our knowledge been reported Ferrofluids have been made that are colloidal suspensions of tiny solid ferromag netic particles 100 A in diameter suspended in a liquid medium Two mbture a Two phase YqF 0 2 GdF e02 4000 3000 1000 b Single phase solid solution Y sad sF 6O Figure 5 A portion of the X ray powder diffraction patter of a a two phase mixture of Y FesO 2 GdaFe O and b a single phase solid solution compound Y 5Gdy sFes042 lattice parameters of Y Fes0 2 and GdzFes0 2 differ the positions of the diffraction peaks also should differ Thus in a two phase mixture formed for this purpose by physi cally mixing equal amounts of Y Fes0O and GdsFes0 a the diffraction pattern consists of two distinct patterns super imposed as shown in Figure 5a However the solid so
51. eros de los compuestos preparados sabiendo que los dos grupos nitrato est n enlazados al n quel 3 Registrar e Interpretar los espectros IR en KBr de los compuestos preparados Bibliograf a Nakamoto K Infrared and Raman Spectra of Inorganic and Coordination Compounds Part A Theory and Applications in Inorganic Chemistry Wiley 1997 Ver p ginas siguientes Extraidas del texto de K Nakamoto Infrared and raman spectra of inorganic and coordination compounds 4th edition John Wiley and Sons New York 1986 11 16 Oxo Anions as Ligands 489 The Nitrate lon This ion has several structural roles as follows o M M o q A o m Sno i M Sb a Nu o M o Yo N A o So M M eee 7 go N ON EN O o O M Wa n M M o i z ONO o o Ox O N LI SA AI AA ar Aga ae ae v Ps M The most common forms of the nitrate ion are symmetrical bidentate followed by 1 The free NO ion has relatively high symmetry D34 thus its ir spectrum is fairly simple The totally symmetric N O stretching mode is not ir active but the doubly degenerate N O stretching mode gives rise to a strong band at 1390 cm There are also two ir active deformation modes one of which is doubly degenerate at 830 and 720 cm When NO is coordinated its effective symmetry is reduced causing the degeneracies to split and all modes six to be ir active Hence it is possible to distinguish between ionic and coordinated NO groups
52. estuiviera accesible o localizado en ese momento Servicio de emergencias 112 desde cualquier tel fono En cualquiera de los casos se deber indicar Ubicaci n de la emergencia edificio piso sala Tipo de emergencia Si hay personas accidentadas 3 SOCORRER Act e sin precipitaci n Si hay alguna persona accidentada no la mueva sin conocer antes las posibles lesiones Permanezca sereno y tranquilice al lesionado hasta que llegue la ayuda de un profesional m dico PRIMEROS AUXILIOS Para poder reaccionar con rapidez en caso de accidente hay que conocer en primer lugar la localizaci n exacta de extintores duchas y lavaojos En todos los casos hay que avisar inmediatamente al profesor A continuaci n se enumeran algunas contingencias ante las que debe procederse con toda rapidez como se indica 1 Proyecci n de compuestos a los ojos Enju guense stos inmediatamente con mucha agua ducha lavaojos durante al menos diez minutos e informe al profesor de lo sucedido Si las molestias persisten o existe evidencia de da os es necesario consultar a un oftalm logo 2 Vertido de productos sobre la piel Retirar la ropa contaminada y proceder al lavado inmediato con mucha agua de la zona afectada Cuando se produzcan contactos irritantes de cidos con la piel seque la zona afectada y luego lave r pidamente con soluci n de bicarbonato s dico al 5 10 y posteriormente con abundante agua Si la irritaci n fue caus
53. experimental inves tigations and the Dreyfus Foundation and the National Science Foundation grant USE 9150484 for financial support Literature Cited 1 Shakhashiri B Z Dirreen G E Williams L G Y Chem Educ 1980 57 373 374 2 a Vidyasagar K Gopalakrishnan J Rao C N R J Solid State Chem 1985 58 29 37 b Robbins M Wertheim G K Storm A R Buchanan D N E Mat Res Bull 1972 7 233 239 3 Gordon A J Ford R A The Chemists Companion Wiley New York 1972 pp 451 4652 4 a Wang F F Y In Treatise on Materials Science and Technology Vol 2 Herman H Ed Academic Press New York 1973 pp 279 384 b Geller S In Physics of Mag netic Garnets Paoletti A Ed North Holland Publishing Co Amsterdam 1978 pp 1 55 c Khattak C P Wang F F Y In Handbook on the Physica and Chemis try of Rare Earths Vol 3 Gechneidner K A Jr Eyring L Eds North Holland Publishing Co Amsterdam 1979 pp 525 607 5 Weidenborner J E Acta Cryst 1961 14 1051 1056 6 Harrison G R Hodges L R Jr J Appl Phys 1962 33 1975 1376 Volume 71 Number 8 August 1994 703 30 4 B Inserci n de hidr geno en tri xido de wolframio El tri xido de wolframio tiene una estructura formada por octaedros WO que comparten v rtices En los huecos de esa estructura se pueden alojar distintos cationes para dar lugar a especies no estiquiom tricas de f rmula M WO
54. hacer una evaluaci n de todos los riesgos y tomar las medidas necesarias para la prevenci n de accidentes As mismo deben conocer las instrucciones de operaci n de los equipos y las propiedades de los materiales que vayan a usarse 6 El laboratorio cuenta con Duchas y lavaojos extintores de incendios botiqu n de primeros auxilios recipientes met licos conteniendo arena u otro material inerte Antes de empezar a trabajar todos deben conocer la ubicaci n de los elementos y dispositivos de seguridad Indumentaria y precauciones personales 7 Las gafas de seguridad han de usarse en el laboratorio en todo momento Protegen los ojos de proyecciones y salpicaduras Nunca deben usarse lentes de 56 10 11 10 11 12 13 14 15 contacto stas pueden ser muy peligrosas en caso de accidente porque no pueden quitarse con rapidez las sustancias corrosivas pueden situarse por debajo de la lentilla y permanecer junto al tejido que da an m s tiempo Es obligatorio el uso de una bata de laboratorio que debe llevarse siempre abrochada y que protege el resto de la ropa y la piel No es recomendable el uso de sandalias o zapatos abiertos que no protegen los pies El pelo largo debe estar siempre recogido No est permitido comer beber o fumar en el laboratorio por el peligro de contaminaci n o incendio que supone Nunca se debe trabajar solo en un laboratorio con objeto de poder recibir ayuda en caso de ac
55. iley 1991 Woollins J D Ed Inorganic Experiments VCH Weinheim 1994 Angelici R J T cnicas y S ntesis en Qu mica Inorg nica Revert 1979 Brauer G Qu mica Inorg nica Preparativa Revert 1958 2 PREPARACI N Y CARACTERIZACI N DE COMPLEJOS DE N QUEL Los complejos mononucleares de nigue II presentan una amplia variedad de estructuras siendo las m s habituales la octa drica la tetra drica y la planocuadrada Los complejos octa dricos y tetra dricos tienen generalmente dos electrones desapareados mientras que los planocuadrados son diamagn ticos Muchos ligandos utilizados en qu mica de la coordinaci n pueden actuar nicamente como monodentados por ejemplo PPh3 sin embargo hay otros que pueden enlazarse de diferentes formas El i n NO3 puede encontrarse libre sin coordinarse simetr a D3h pero tambi n puede actuar como ligando monodentado coordin ndose a trav s de uno de sus ox genos o bidentado coordin ndose a trav s de dos de sus ox genos en complejos mononucleares Por otro lado hay ligandos que pueden coordinarse a trav s de tomos diferentes ste es el caso del i n NCS que puede coordinarse a trav s del azufre del nitr geno o a trav s de ambos actuando como puente entre dos metales Esta pr ctica propone la s ntesis y la caracterizaci n estructural de dos complejos de niquel II La determinaci n de las geometr as de los complejos y el modo de c
56. in capsule avail able at a pharmacy counter before carrying out the mag netic tests Note that if a press is not available the loose powder may require longer or repeated firings in order to complete the reaction X Ray Powder Diffraction optional Some instructors may wish to have their students verify the identity of the olive green solid by X ray powder dif fraction X ray powder diffraction patterns of the samples were recorded from 10 100 28 on a Nicolet X ray powder diffractometer The powder diffraction pattern ofthe sam ple with the nominal composition Y sGd sFesO s is shown in Figure 1 The major product of the reaction was the gar net phase R Fes0Oy2 R rare earth element The peaks indicated with an asterisk in Figure 1 are due to RFeO R rare earth element which is a common impurity in sam ples of RgFe O12 Grinding the olive green solid repelletiz ing and firing a second time at 900 C or higher tempera tures for 24 h led to a noticeable decrease in the intensities of the peaks of the impurity phase in the dif fraction pattern It should be noted that the presence of a small amount of the RFeO phase in the samples does not adversely affect the investigation of the magnetic proper ties in this experiment To obtain the lattice parameters for the samples silicon was added as an internal standard prior to collecting the diffraction data and the line positions were corrected for systematic errors by
57. k No xD YY N N NX Ni HCI g NH PF A x g SEG AL a NH NZ ya ate l 8 NH Figura 1 Una vez sintetizado el macrociclo es posible aislar el ligando destruyendo el complejo haci ndolo reaccionar con HCl para lo que es necesario generar una corriente de 46 HCl gas Una vez aislado el macrociclo puede ser utilizado para sintetizar complejos con otros metales Procedimiento experimental All reagents and solvents are used as supplied except 1 2 diaminobenzene o phenylenediamine that should be purified by a single recrystallization from EtOH in the presence of decolorizing charcoal or by sublimation Dry the n butanol over 4 molecular sieves Complejo macroc clico de n quel Place 2 00 g of Ni OAc 2 4H 0 8 03 mmol 1 73 g of o phenylenediamine 1 60 mmol 35 mL of dry butan 1 ol 1 7 mL of 2 4 pentanedione 1 66 mmole and a stirring bar in a 100 mL round bottom flask Adapt a reflux condenser to the flask and set 1t in a heating mantle Bring the mixture to a brisk reflux and stir for 1 5 hours noting any color changes Then concentrate the solution by slow distillation of the BuOH at ordinary pressure to aprox 20 mL and reflux it 35 minutes more Remove the flask from the heat source and allow it to cool until it is just warm to the touch Add 30 mL of methanol and cool the mixture in an ice salt bath for at least 15 min to precipitate the nonpolar macrocyclic complex Filter the solid a
58. l y 21 mL de la disoluci n acuosa de hidr xido de sodio El compuesto se obtuvo como un s lido blanco cristalino Cuestiones 1 Discutir el papel del acetato de paladio en la reacci n Buscar en la bibliograf a recomendada un ciclo catal tico que permita explicar el mecanismo de la reacci n 2 Buscar un ejemplo de aplicaci n de la reacci n de Heck a la s ntesis de un producto natural o a un producto de importancia industrial Bibliograf a T Mizoroki K Mori A Ozaki Bull Chem Soc Jpn 1971 44 581 b R F Heck J P Nolley Jr J Org Chem 1972 14 2320 2322 Ver revisiones en a S Br se A de Meijere en Metal Catalyzed Cross Coupling Reactons Eds A de Meijere F Diederich Wiley VCH New York 2004 cap tulo 5 b I P Beletskaya A V Cheprakov Chem Rev 2000 100 3009 3066 Una descripci n de estos experimentos se puede encontrar en An Quim 2009 105 2 34 5 B Oxidaci n catal tica de trifenilfosfina por un dioxocomplejo de molibdeno VD La oxidaci n de ciertos sustratos catalizada por oxocomplejos de molibdeno VI tiene mucho inter s por estar involucrada en procesos biol gicos importantes La pr ctica consiste en la preparaci n de dos complejos de molibdeno VD MoO CL DMSO y MoO acac Posteriormente se analiza su capacidad como catalizadores en la oxidaci n de trifenilfosfina Experimental Preparaci n de MoO CL DMSO En un tub
59. l times Enough methanol should be present in the flask to cover the salt Add triethylamine dropwise to the suspension and swirl Filter the free yellow macrocycle wash with 5 mL of methanol and air dry Record the IR spectrum Reacci n de Cu O CMe H O con el macrociclo Charge a 10 mL round bottom flask with Cu OAc H O 0 1 g 0 6 mmol a stirring bar and acetonitrile 4 mL Attach a condenser and reflux the suspension until all the Cu OAc H O dissolves Remove the heater and with a micropipete add slowly a mixture of the macrocycle 0 1 g 0 56 mmol acetonitrile 2 mL and triethylamine 0 20 mL Reflux the resulting dark green solution for about 10 min then cool to room temperature and finally keep it in an ice bath for 20 min Filter the dark green microcrystalline solid and wash it with a 2 mL of acetonitrile and then 2 mL of ether NOTA Procedimiento para generar una corriente de HCI Debe prepararse en la vitrina el montaje que se describe a continuaci n y que puede verse en la figura adjunta El mismo montaje puede servir para dos alumnos El embudo de adici n A se coloca perfectamente ajustado sobre el kitasato B cuyo tubo de desprendimiento conduce a un frasco lavador de seguridad C que a su vez conduce a un matraz D sumergido en un ba o de hielo Hay que asegurarse que las uniones est n perfectamente ajustadas para que no se produzcan fugas de gases 48 A debe contener 20 mL de H2SO4 concentrado
60. lution compound Y15Gd 5Fe5O12 should have a single lattice pa rameter that is intermediate between the pure yttrium containing material and the pure gadolinium containing material The diffraction pattern ofthe solid solution com pound should consist of one set of peaks that are midway between the two sets for the pure materials This is shown in Figure 5b The point should be made to students that a two mixture such as that described in Figure 5a could be physically separated into the two components pro vided that one had tweezers small enough to pick out the particles of pure Y Fe O z and leave the pure Gd Fe502 behind However in practice this physical separation is impossible to carry out in most cases so we must design the syntheses to lead to a single phase product Magnetic Properties Electrons in a solid can behave cooperatively leading to different properties from those observed in the gas or liq uid states An excellent example of cooperative behavior in solids is ferromagnetism The difference between simple paramagnetism and ferromagnetism is shown in Figure 6 Unpaired electrons or spins are depicted in this figure by Volume 71 Number8 August 1994 699 26 arrows There are unpaired spins in a simple paramagnet Fig 6a but in the absence of a magnetic field the spins are oriented randomly relative to one another due to ther mal motion In a ferromagnet the unpaired electrons com municate with one an
61. me results obtained by Sabatini and Bertini The M NCS group is linear or bent while the M SCN group is always bent This seems to suggest that the following resonance structures are predominant in each case 11 188 INFRARED SPECTRA M NCS Group M SCN Group M N C S i Ss C N N C S M Pecile has noted that the integrated intensity of the CN stretching band can also be used to distinguish two linkage isomers Clark and Williamst have obtained the infrared spectra of tetrahedral M NCS L and octahedral M NCS L type complexes M Fe Co Ni etc L pyridine etc and discussed stereochemistry from infrared spectra A similar study has been made by Nelson and Shepherd Bennett et al have obtained the infrared spectra of Cr NCS L where L is an amine or phosphine and have assigned the Cr N and Cr L stretching bands in addition to the NCS group vibrations In M NCS L type com plexes in which M is Pt II or Pd TI the NCS group is S bonded if L is an amine and N bonded if L is a phosphine This is because a strong n acceptor such as a tertiary phosphine makes the d orbitals of the metal less available for bonding with the z orbitals of sulfur Jennings and Wojcicki obtained the infrared spectra of square planar Rh CO NCS L Rh NCS L3 Rh CO NCS and Rh NCS L4 type complexes in TABLE IIT 24 VIBRATIONAL FREQUENCIES OF ISOTHIOCYANATO AND THIOCYANATO COMPLEXES C
62. mposition Acetyl Diacstyl Reaction Time Ferrocene Ferrocene Ferrocene Other 0 1 min trace 0 5 min I 1 5 min trace trace 10 min trace 25 min water and air dry Dissolve a small amount of the dry solid in 5 ml of methanol filter and separate by tle and lc Results and Discussion Ferrocene acylates readily yielding a variety of products as is in dicated in Figure 1 A typical chromatogram depicting the separation of ferrocene I and two major acylation products acetylferrocene TI and 1 1 diacetylferrocene III is shown in Figure 2 Under reverse phase conditions the most polar compound IJI elutes first while the relatively non polar ferrocene I which is adsorbed more strongly on the non polar packing elutes last The separation is complete in less than 10 min allowing many injections during a single laboratory session Table 1 summarizes the results of the lc analysis of reactions quenched at different times and Table 2 lists k and Ry values for 1To extend column life all samples should be filtered prior to le separation 2 k the capacity factor may be defined in terms of the difference between the time required for a component to travel the length of the column and the time to required for solvent or other non retained molecules to traverse the column divided by ty See Figure 2 44 ferrocene and its mono and
63. nd wash 1t with methanol about 2 x 10 mL the washings should be colorless to pale green The dark purple microcrystalline macrocycle is generally obtained in a 37 40 yield Retain a small sample of product for IR analysis Use the remaining product to synthesize the free macrocycle as described below Preparaci n de H Macrocycle NiCl4 Prepare a suspensi n of 1 0 g of the nickel complex in 30 mL of ethanol in a 100 mL round bottom flask Bubble HCl gas through the suspension at a moderate flow and stir it from time to time See note at the end of the experimental part Caution the 47 mixture gets quite warm Once a copious turquoise precipitate forms filter 1t off and wash it with ethanol 2 x 5 mL and ether to obtain about 95 yield of product Aislamiento de la sal del macrociclo Mac H Mac BF4 gt Dissolve the turquoise H4 Mac NiCly salt in 10 mL water Occasionally white water insoluble impurities are present at this stage and can be removed by filtration Add 1 0 g of solid NH4BFy to the filtrate and swirl until a large amount of white precipitate forms Filter the H4 Mac BF in a sintered glass filter and wash with water until the product is pale green In this step the NH4 NiCl byproduct needs to be washed away to prevent nickel from re coordinating into the macrocycle upon basification Transfer the sticky solid to a 25 mL Erlenmeyer flask rinsing the sintered glass filter with methanol severa
64. now M R 3 Bell C J Synthesis and Physical Studies of Inorganic Compounds Pergamon Oxford Inorg Chem 23 J Amer Chem Soc 106 5478 1984 E Literature Cited 55 AP NDICE 1 NORMAS GENERALES DE SEGURIDAD E HIGIENE EN UN LABORATORIO QU MICO En un laboratorio de Qu mica se manipulan sustancias y se realizan operaciones que pueden resultar peligrosas si no se realizan adecuadamente Es necesario por consiguiente extremar las precauciones y actuar conociendo los riesgos de las Operaciones que se realizan para prevenir y evitar los peque os accidentes que pueden producirse Conocer el contenido de este apartado es por ello fundamental antes de Iniciar el trabajo en un laboratorio A continuaci n se indican algunas normas y recomendaciones a tener en cuenta NORMAS GENERALES l El alumno seguir minuciosamente el gui n de pr cticas y en su caso los consejos del profesor al llevar a cabo un experimento 2 El alumno no debe realizar nunca experimentos diferentes a los se alados en el gui n de pr cticas salvo consulta previa con el profesor y consentimiento de ste 3 Ante cualquier percance o accidente avisar inmediatamente al profesor 4 Durante la jornada de trabajo las puertas de acceso a los edificios deben permanecer abiertas y libres de obst culos Mantenga despejadas las zonas de entrada salida y circulaci n en el laboratorio 5 Antes de iniciar un experimento los que participen en l deben
65. o de ensayo se colocan 0 25 g de NH M0 0 4H 0 1 g de agua y 2 g de HCI del 37 La mezcla se calienta con agitaci n durante 10 minutos a 100 C en un ba o de agua y la disoluci n resultante se enfr a a temperatura ambiente Posteriormente se a aden con agitaci n 0 5 g de dimetilsulf xido y la mezcla se enfr a de nuevo El precipitado blanco se filtra se lava con acetona 2 x 1 mL y posteriormente con ter et lico 2 x 1 mL y finalmente se seca por succi n Preparaci n de MoO acac En un tubo de ensayo se colocan 0 25 g de MoO 0 4 g de agua y 0 4 g 5 5 mmol de NH del 24 La mezcla se agita hasta obtener una disoluci n incolora produci ndose una reacci n exot rmica A continuaci n se a aden 0 75 g de 2 4 pentanodiona y aunque la mezcla se agita se mantienen dos fases Finalmente se adiciona 1 g de cido n trico al 63 produci ndose un proceso exot rmico La mezcla se enfr a a temperatura ambiente manteniendo la agitaci n precipitando el producto como un polvo amarillo Se recoge por filtraci n y se lava sucesivamente con agua 4 x 2 mL etanol 2 x 2 mL y dietil ter 2 x 2 mL Finalmente se seca por succi n Ensayos de oxidaci n catal tica de la trifenilfosfina En un tubo de ensayo se colocan 50 mg de MoO CL DMSO 0 5 g de trifenilfosfina y 2 5 g de dimetilsulf xido La mezcla se calienta a 100 C durante 15 minutos en una campana La disoluci n obtenida se a ade sobre 12 mL de NaO
66. o de un tubo de cloruro c lcico se a aden gota a gota 2 mL de cido ortofosf rico La mezcla se calienta en ba o de agua a 100 C durante 30 minutos y a continuaci n se vierte sobre 80 g de hielo picado con agitaci n Cuando todo el hielo se haya fundido la disoluci n se neutraliza con hidrogeno carbonato s dico s lido La mezcla se enfr a en ba o de hielo durante 20 minutos y se recoge por filtraci n el 40 producto como un s lido amarillento que posteriormente se seca en un desecador de vac o Cuestiones y experimentos adicionales 1 Describir las ecuaciones de todas las reacciones que tienen lugar en cada una de las s ntesis realizadas Calcular los rendimientos obtenidos en la preparaci n del ferroceno y acetilferroceno 2 Describir detalladamente la estructura del ferroceno y discutir brevemente el enlace 3 En un tubo de ensayo a adir 0 02 g de ferroceno a 2 mL de agua y despu s 2 mL de cido n trico concentrado Posteriormente agitar el tubo durante unos dos minutos 4 Observar e interpretar el resultado obtenido 5 Discutir los espectros de IR y de IH NMR tanto del ferroceno como del acetilferroceno Bibliograf a ver en p ginas siguientes a C Elschembroich Organometallics Wiley VCH Weinheim 2006 b H McKone J Chem Ed 1980 57 5 380 381 41 316 15 a n Donor r Acceptor Ligands Their actual goal was the synthesis of fulvalene FeClg 2 C HgMgBr
67. of Y Fes0y2 can be picked up by the cow magnet at room temperature dry ice temperature and liquid nitrogen temperature A plot of the magnetization of Y FesO 2 ver sus temperature shown in Figure 8 agrees with this qualitative behavior At the other extreme in the solid solution Gd Fe5O1 has the same net five unpaired electrons from the two iron sublattices But in addition each Gd ion there are three in the garnet formula has seven unpaired electrons The electrons in the gadolinium sublattice order antiferromag netically antiparallel to the net five unpaired electrons of the tetrahedral iron This suggests that the magnetic mo ment of Gd Fes0 2 should be 16 3 x 7 5 unpaired elec trons This is true if the moment is measured at very low temperatures However the gadolinium sublattice and the iron sublattice thermally randomize at different tempera ture dependencies The result is a compensation tempera ture Tromp Where the net magnetization is zero In Gd Fe5012 the compensation temperature is just below The identity of the subscripts is derived from the standard notation for the garnet formula CxA2D30 2 where C represents the dodeca hedral site A represents the octahedral site and D represents the tetrahedral site Gd3Fes012 Temp K 150 200 250 300 Temp K Figure 9 The temperature dependence of the magnetization per gram for GdyFes0 2 The inset contains an enlargament of the region from 260
68. om the 1H NMR spec trum 200 MHz spectrometer D20 N deuterated shifts rel ative to DSS mainly two overlapping quartets are observed associated with AB or AA BB patterns of the cap and en methylene groups Figure 2 Electrochemistry In water a reversible 1 e couple at 0 20 V versus SCE mercury electrode 0 1 M NaClO electrolyte is observed for Co dinosar in both de at DME and cyclic at HMDE voltammetry Further an irreversible 8 e re duction occurs in neutral solution at 0 7 V due to reduction of both NOz capping groups to NHOH 4 e each Cyclic voltammetry at a hanging mercury drop electrode clearly defines the reversible nature of the first Co III Co II re duction and the irreversible nature of the second NO gt NHOH reduction By comparison Co en 33 exhibits only a single wave at 0 41 V and this reduction is not fully re versible Detailed electrochemical studies of a range of such macrobicycles have appeared 8 Further Experiments Reduction of the Co dinosar 3 complex chemically with Zn HCI and air oxidation subse quently yields the Co diamsarH3 Cl complex from HC solution with fully reduced NH3 groups on the apical caps 9 The absence of the NO groups can be readily established by IR spectroscopy and electrochemistry The original syn thesis can be performed with optically active Co en g whence the product is optically active Reduction with Zn HCl and s
69. ond 2 6 g portion of sodium acetate trihydrate dissolved in a minimal amount of water Heat the resulting mixture directly on a hotplate for 10 minutes at about 70 C put a thermometer directly in the reaction flask and then set aside to cool to room temperature Collect the dark 15 brown precipitate on a B chner funnel Use small portions of deionized water 2 x 5 mL to wash any remaining crystals out of the flask Allow the product to dry until the next lab period and then weigh the dry final product to determine the yield of dry product 3 D Preparaci n de Fe acac Add approximately 1 3 g of Fe NO3 3 9H20 into a 50 mL Erlenmeyer flask and dissolve in 7 mL of distilled water Drop in a magnetic stir bar stir the solution and add a mixture of 1 0 mL of acetylacetone in 7 mL of methanol Next add a solution containing 1 3 g of sodium acetate trihydrate in 7 mL of distilled water and briefly heat the mixture on a hotplate until some of the methanol has boiled away you should see the volume of the reaction mixture go down Cool to room temperature and then place in an ice bath for about 15 minutes Filter the red crystalline solid using a B chner funnel wash the flask and crystals using 2 x 5 mL of deionized water Allow the product to dry until the next lab period and then weigh the dry final product to determine the yield of dry product Cuestiones y experimentos adicionales 1 Ajustar las reacciones que tienen lugar en c
70. oordinaci n de los ligandos se realizar sobre la base de los resultados experimentales de espectroscopia vibracional IR Procedimiento experimental Preparaci n de Ni NCS PPh Una mezcla de nitrato de n quel hexahidratado 1 4 g tiocianato pot sico pulverizado 1 4 g y butanol 75 mL se calienta a reflujo durante dos horas La mezcla amarillenta resultante se enfr a y se filtra obteni ndose una disoluci n verde Esta se calienta a ebullici n y se a ade sobre una disoluci n tambi n a ebullici n de trifenilfosfina 2 623 g en butanol 25 mL Por enfriamiento lento se obtiene el producto buscado en forma cristalina que se filtra se lava y se seca por succi n Preparaci n de Ni NO PPh Sobre una disoluci n de nitrato de n guel hexahidratado 1 4 g en 1 5 mL de agua se a aden 25 mL de cido ac tico glacial se a ade otra caliente de trifenilfosfina 2 6 g tambi n en cido ac tico glacial 25 mL La disoluci n resultante se mantiene templada por calentamiento suave y con agitaci n apareciendo paulatinamente el producto como un s lido verde La mezcla se deja en reposo 24 horas y se filtra el producto obtenido que se lava dos veces con acetona y se seca por succi n Cuestiones y experimentos adicionales 1 Describir las reacciones globales que tienen lugar en cada una de las s ntesis realizadas y calcular los rendimientos de los productos sintetizados 2 Indicar todos los posibles is m
71. other and align in large regions known as magnetic domains Fig 6b The sizes of the do mains vary with the material but are typically on the order of hundreds of angstroms In the absence of a magnetic field the composite spins of individual domains are or dered randomly so that the net magnetization of a macro scopic piece of ferromagnet is zero The application of a magnetic field Fig 6c aligns all of the spins in the direc tion of the magnetic field leading to an overall net mag netization The application of a magnetic field to a param agnet also would align the spins in the direction of the magnetic field but the overall magnetization is less than in the case of a ferromagnet because there is no communi cation or magnetic ordering between the spins The observed temperature dependent magnetic behav ior of a ferromagnet is derived from the interplay of ther mal energy which randomizes the spins and the energy stabilization gained by aligning the spins in the ferromag netic state Ferromagnetism is an example of a solid state phase transition with a characteristic transition tempera ture Above an ordering temperature known as the Curie The application of magnetic properties in technology relies on the existence of domain walls and the ability to control the movement of the domain walls For example in permanent magnets the domain walls are not moved easily However in the promising technology of magnetic bubble
72. r financial support A198 Journal of Chemical Education Literature Cited 1 a Holm R H Chem Rev 1987 67 1401 and references therein b Holm R H Count Chem Res 1200 100 183 aud referances therein c Enemark F H Young C G Adv Inorg Chum 1991 40 1 and references therein 2 a Roberts S A Young C G Kipke C A Cleland W E Je Yamanouchi K Carducei M D Enemark J H Inorg Chem 1990 29 3650 b Arzoumanian H L pez R Agrifogho G Inarg Chem 1894 33 3177 c Axnkiz F J Aguado R Mart nez do Narduya J M Folrhedror 1994 13 3515 3 rntiz F J Inorg Synih in presa A Butcher R J Gunz H P MacLagan R G A R Kipton H Powell J Wilkins C J Hian Y 3 4 Chem Soc Dalton Trans 1975 1223 5 Uoddington J M Taytor M J Chem Soc Dalton Trans 1000 1 41 6 Taylor M J Jirang W Rickard C E F Polyhedron 1899 12 1433 7 Arete Ts many R Sanz Aparicio J Martinez Ripoll M Polyhedron 1994 13 8 Greenwood N N Barnshaw A Chemistry of the Elements Pergamon Press Oxford 1984 from Journal of Chemical Education Vol 72 Page A7 A8 January 1995 Copyright 1996 by the Division of Chemical Education of the American Chemical Society and reprinted by permiesion of the copyright owner Microscale Synthesis of MoO2 acac 2 Francisco J Arnaiz Laboratorio de Quimica Inorganica Universidad de Burgas 09001 Burgos Spain
73. re dependent magnetization of the octahe dral sublattice and M 7 represents the temperature de pendent magnetization of the dodecahedral sublattice Each term such as Ma T represents a sum of the mag netic moments at that particular crystallographic site i e There are three tetrahedral sites in each formula unit The negative signs in eq 1 result from the fact that the spins in the octahedral sublattice M and the spins in the dodecahedral sublattice M align parallel to each other but antiparallel to the spins in the tetrahedral sublattice Ma The different magnetic sublattices can have different temperature dependencies for their magnetization that may lead to M 7 0 at a specific temperature below T This temperature is the compensation temperature Teamp For the material Y FesO s the Fe ions with five un paired electrons in the octahedral holes order antiferro magnetically spins aligned antiparallel with the Fe ions also with five unpaired electrons in the tetrahedral holes However because there are three tetrahedral sites and two octahedral sites in the garnet formula there is a net magnetic moment of five unpaired electrons There is 100 0 80 0 60 0 40 0 Magnetization per gram 20 0 0 0 0 50 100 no magnetic contribution from the closed shell yttrium ion Thus YsFe 012 is strongly magnetic at all temperatures This behavior can be demonstrated by the fact that the pel let
74. roperties of a solid depend on composition the presence of magnetic ions on the underlying crystal structure the geometrical arrangement of the ions in three dimensions and on temperature In order to elimi nate the influence of structure and to isolate the effects of composition and temperature on magnetic properties ide ally we would like to change the composition of a mag netic solid without disrupting the crystal structure In other words we would like to study the magnetic proper ties of a solid solution In this paper we will describe a general synthesis for compositions in the solid solution series Y Gd3 FesO1 0 lt x lt 3 and a simple demonstration that illustrates the dif fering magnetic properties of these materials This experi ment serves several purposes Students gain experience in synthetic techniques commonly used to prepare many solid state oxides that are important in materials chemis try today If X ray powder diffraction is available the X ray diffraction patterns can be analyzed to discuss the structural characterization of solid solutions and illustrate the evolution of the lattice parameter with composition Fi nally these materials display some unique magnetic prop erties that open the discussion to cooperative effects in a and the applications of magnetic materials to tech nology Experimental Synthesis Compounds in the Y Gdz_ FesO 12 0 lt x lt 3 solid solution series were synthe
75. rrocene with product identification by thin layer and open column chromatography is currently a popular undergraduate experiment 3 10 Haworth and Liu recently reported a high performance liquid chromatographic lc separation of acylated ferrocenes using normal phase conditions of silica packing and an ether methanol mobile phase 11 12 The increasing use of lc in separating components in organic reaction mixtures encour aged us to investigate incorporating this lc separation of fer rocenes into our undergraduate laboratory However nor mal phase Ic has several disadvantages over the more ver satile reverse phase chromatography The former requires relatively long column equilibration times and generally ne cessitates using non aqueous mobile phases We have devel oped a reverse phase separation of these ferrocenes using a Cia bonded to silica column u BONDAPAK C1g Waters Associates and a far less bothersome mobile phase of meth anol water A complete introduction to reverse phase le may be found in references 13 and 04 Instrumentation A Waters ALC GPC 204 Liquid Chromatographic with a Model U6K Injector and a Houston Omni Scribe Model 5211 1 Recorder were used The prepacked analytical column consisted of Cia bonded to 10 um silica particles Waters Associates Inc Milford MA 01757 and the mobile phase was a mixture of methanol water in a ratio of 3 1 The flow rate was 0 9 ml min and the absorbance dete
76. rti M C Bandyopadhyay D Inorg Synth 1992 29 12 38 2 Complexes of Sulfoxides and Related Componnds Cotton et al studied the infrared spectra of sulfoxide complexes to see whether coordination occurs through oxygen or sulfur The electronic struc ture of sulfoxides may be represented by a resonance hybrid of the structures R R S ys 53 am SE M p S RO R I lI If coordination occurs through oxygen contribution of structure JI will decrease and result in a decrease of the SO stretching frequency If coordina tion occurs through sulfur contribution of structure I will decrease and may result in an increase of the SO stretching frequency Aa TABLE III 34 SHIFTS or SO STRETCHING BANDS IN DPSO AND DMSO COMPLEXES CM 1012 1035 O 23 E Mg ID 1012 23 Mandi 983 991 45 41 Zn 987 988 47 Fei 987 48 Ni 1D 979 982 55 45 Coll 978 980 56 1 Cuil 1012 948 23 87 58 AIGH 942 93 a Fe III 931 104 The far infrared spectra of DMSO complexes have been studied by Johnson and Walton who assigned the M O stretching bands at 500 400 cm The S bonded DMSO complexes PHII and Pd ID also exhibit a strong band in the same region Hence it is difficult to differentiate the O 39 6 ESTUDIO DE LA REACTIVIDAD DE UN LIGANDO COORDINADO PREPARACI N DE FERROCENO Y ACETILFERROCENO El descubrimiento en 1951 de bis ciclopentadienil hierro
77. s are the two C C bonds in the ring 17 248 INFRARED SPECTRA The infrared spectra of metal acetylacetonate complexes have been studied extensively In 1956 Mecke and Funck assigned the infrared spectra of acetylacetone keto and enol forms and its metal complexes on an empirical basis In 1960 Nakamoto and Martell carried out an approximate normal coordinate analysis on Cu acac At the time of this earlier research no spectral data were available below 400 cm and no isotopically substituted acetylacetonato complexes were studied Since then a number of investi gators608 6108 have extended their measurements to the far infrared region The spectra of metal complexes containing C and O labeled acety acetones have been obtained 912 A rigorous normal coordinate analysis considering all the atoms in the molecule has been made for M acac and M acac 3 type complexes Table III 49a lists the observed frequencies band assignments and M O stretching force constants obtained by Mikami et al 513 Figure III 33a shows the infrared spectra of six acetylacetonato com plexes The nature of the 1577 and 1529 cm bands of Cu acac has been a subject of controversy Originally Nakamoto and Martell assigned the former to a C C stretching and the latter to a CO stretching mode Mikami et al also gave similar assignments although they showed that these two modes are coupled slightly with each other However
78. s dominios magn ticos del hierro en entorno octa drico y del gadolinio son paralelos sus momentos magn ticos individuales se suman y el del hierro en entorno tetra drico es antiparalelo a ellos Por lo tanto la magnetizaci n total ser proporcional a la cantidad de tomos que hay de cada clase Ga Feo y Fe por la cantidad de electrones desemparejados de cada uno y contribuir positiva o negativamente seg n su orientaci n relativa 3 x x7 2x5 3x5 El experimento se realizar coordinadamente en grupos de cuatro alumnos de forma que cada uno de los cuatro sintetice una muestra con un valor diferente de x 0 4 1 2 1 8 y 2 7 para obtener granates con distinto comportamiento magn tico La s ntesis se efect a mediante el m todo del precursor Se forma un hidr xido mixto conteniendo los tres metales con lo que se obtiene una sustancia homog nea que luego se transforma en el granate por calefacci n 20 Procedimiento experimental You will prepare one member of the Y Gd FesO 0 lt x lt 3 family that is you will be assigned a particular value of x A description of the synthesis of Y Gd Fe O via a mixed metal hydroxide precursor follows Other compositions in the series can be prepared by varying the volumes of Gd NO and Y NO used in such a way that the amount of Gd NO plus the amount of Y NO totals 6 mL Place 10 mL of 0 3 M FeCl in a beaker Add 3 mL of 0 3 M Gd NO solution
79. sar 1 8 di nitro 3 6 10 13 16 19 hexaazabicyclo 6 6 6 icosane The described synthesis from Co en 33 can be completed within 2 to 3 b and is inexpensive and safe Various aspects of visible infrared and nuclear magnetic resonance spectroscopy and of electrochemistry and optical activity can be incorporated into the program as desired Synthesis of the Macrobicyclic Complex Co en a Br3 2 5 g and anhydrous NaCO 1 5 g are dissolved in water 90 mL in a 200 mL beaker and nitro methane 5 mL and 37 aqueous formaldehyde 40 mL added Caution Reaction should be performed in a fume hood After stirring briefly t mix reagents the solution is placed not stirred in a waterbath and maintained at 35 40 C for approximately 1 to 11 h The color rapidly darkens from yellow to brown and after 1 h an appreciable amount of yellow crystals form The solution is stirred briefly and occasionally with a glass rod to help induce crystallization The solution is removed from the waterbath after the 111 h period and cooled immediately to 5 C in an ice bath The crystals are collected on a sintered frit under suction The filtrate is discarded fume hood sink If crystallization upon cooling is not substantial addition of up to an equal volume of ethanol to induce precipitation may be employed but is normally not required The collected solid is dissolved on the frit using portions of hot dilute acetic acid a total of 30 mL of
80. sideraciones generales Todos los reactivos usados son higrosc picos mantener los recipientes que los contienen abiertos el tiempo imprescindible para tomar la cantidad necesaria para el experimento 1 S ntesis del cloruro de tris etilenodiamina cobalto IID Co en 3 Cl5 V2NaC1 3HO Adaptado de Synthesis and Technique in Inorganic Chemistry Girolami Rauchfuss Angelici 1999 En un vaso de precipitados de 100 mL se disuelven 7 0 mL de etilenodiamina en 8 mL de agua Aparte en un Erlenmeyer de 250 mL provisto de una varilla imantada se disuelven 6 g de CoCl gt 6H gt O previamente pulverizado en 16 5 mL de HCl concentrado 37 y se pone a agitar A esta disoluci n agitada se a ade con una micropipeta gota a gota muy despacio la disoluci n de etilenodiamina previamente preparada ATENCI N esta reacci n es muy exot rmica Una vez terminada la adici n se agita la disoluci n resultante diez minutos m s En este punto la disoluci n debe tener un color 51 muy oscuro rosa gris ceo A esta disoluci n se a aden en peque as porciones 8 0 g 200 mmol de hidr xido s dico s lido ATENCI N esta reacci n es exot rmica La disoluci n toma un color azulado Cuando toda la sosa se ha disuelto se a aden 20 ml 20 mmol de per xido de hidr geno al 3 La disoluci n toma un color salm n oscuro Si durante este proceso se ha evaporado agua diluir la disoluci n hasta 50 mL Se debe obtener una disoluci n homog n
81. sized via a mixed metal hydroxide pre cursor 2 A 1M stock solution containing yttrium nitrate was prepared by dissolving Y NO3 5H30 Aldrich 99 9 in deionized water Likewise 1 M stock solutions were pre pared from Gd NO3 6H 0 Aldrich 99 9 and FeClje6H O Alfa ACS grade A description of the synthe sis of Y 5Gd15Fes012 follows Other compositions in the se ries can be prepared by varying the volumes of Gd NO3 3 and Y NO3 used A 3 mL aliquot of 1 M Gd NO solution and a 3 mL ali quot of 1 M Y NO solution were added to 10 mL of 1 M FeCl in a beaker Excess 6 M NaOH 5 10 mL was then added dropwise to the metal ion solution in order to pre cipitate a reddish brown solid After precipitation was complete the solution was decanted and the remaining solid was washed repeatedly with water until the super natant solution no longer tested basic using standard pH paper Then the reddish brown solid was filtered and dried in a drying oven 120 C overnight The resultant powder was pressed into 1 2 in diameter pellets using a standard pellet press and fired in a furnace at 900 C for 18 24 h A visible color change from reddish brown to olive green af ter firing indicated that a reaction had taken place Preparing the material in the form of a pellet is neces sary to carry out the magnetic tests described below If a pellet press is not available we have found that the loose powder can be packed into an empty gelat
82. stitution would then be sur pressed by oxidation to the ferricinium ion FeCp which is inert to attack by elec trophiles That electrophilic substitution of ferrocene does not involve direct participa tion of the metal has been established by the intramolecular acylation of two isomeric ferrocene carboxylic acids It was found that the exo isomer in which the acylium ion cannot directly interact with the metal cyclizes faster than the endo isomer Rosenblum 1966 aa lt gt h En ji b lt gt lt zs i A lt gt LTA CH CHACOOH p gt de CF CO O an o slaw ds lt b This result suggests that electrophilic attack occurs from the exo direction 43 Acylation of Ferrocene Harold T McKone St Joseph College West Hartford CT 06117 Effect of temperature on reactivity as measured by reverse phase high performance liquid chromatography The Friedel Crafts Reaction a widely used synthetic tool is an integral part of most organic laboratory courses For mally benzene was the preferred substrate for this electro philic substitution reaction However recent reports con firming benzene s carcinogenicity necessitate using a safer aromatic compound Ferrocene T is a reasonable alternative since it is relatively non toxic stable more reactive than benzene inexpensive in the quantities needed per student and affords an interesting array of acylation products 7 2 In fact the Friedel Crafts acylation of fe
83. t years to most likely as illustrated in the reaction scheme below The include many examples of macromonocyclic ligands 5 and constraint and ordering of reactants about the metal ion and recently examples of saturated macrobicyclic ligands 6 The the small ring closures involved make the template synthesis latter complexes totally encapsulate the metal ion and are entropically favorable prepared by an organic template reaction about the inert Co en 33 precursor en ethylenediamine H e g H2NCH CH2 NH e g HG M ji LA Wa a NO oo OH NH HN NH NH c CHNO by Sa eee o mo KO H aq base N Q Co dinosar 3 H e HAN NH NH n E SCH NO Co en 3 N p N H o ie CH He zu c mc EN A N m i N M N Bu ec gt Br M HCHO 223 u N N N H H H E IK a OS HN NH NH NH N P HCHO E f 2 Figure 1 Visible absorption spectra of A Co dinosar Bra and B Oofen s NN N N N Bra H H H H H 804 Journal of Chemical Education 54 a NO eo NH HN CE x N de H H 2 B NO This type of synthesis introduces a new class of coordination compounds as direct descendants from classical complexes The synthesis of an aza capped analog of Co dinosar 3 has been described 7 but that synthesis involves an isolation procedure less facile and less suitable for subsequent exper iments than is the case of Co dinosar 3 dino
84. tains mainly OPPha the catalyst and some DMS suggests that Mo V or Mo IV species are not pre sent in significant amounts 8 3 The DMSO solution is poured into sufficient aqueous NaOH so that OPPh3 precipitates as the MoO2Clo DMSO is converted into soluble sodium chloride and molybdate thus avoiding contamination of the OPPhg Final Considerations To highlight the role of the molybdenum complex it is advisable to conduct a blank experiment To minimize 37 the microscale laboratory ASA A AE AN UD SR ASES RS EEE POR CI ENTRE ANO SEI PEE TI TATI SAMA A SE waste the procedure for the preparation of OPPha can be modified so that a solution of PPhg in DMSO is prepared and heated while the catalyst is prepared Then a sample of 0 5 mL is taken off and treated with water to precipi tate the unreacted PPhs which may be further charac terized mp 80 C Finally the catalyst is added and the solution is worked up as described These experiments can be performed in a three hour laboratory period although this catalyzed oxotransfer re action also proceeds at room temperature over a longer pe riod If necessary significant time can be saved by washing the wet OPPh3 with small portions of ethanol e g 2 x 1 mL and diethyl ether e g 2 x 1 mL followed by drying at room temperature although this reduces the yield con siderably Acknowledgment To the editor for helpful comments and to DGICYT Grant PS90 0134 fo
85. te is filtered washed with water 3 x 2 mL and dried in an oven at 120 C for 30 min One obtains 0 49 g 92 yield of white OPPhs This product melts at 157 1 C and displays an IR spectrum characteristie of OPPha e g a strong v P O band at 1182 cm 314 Discussion The above procedures can be explained in a simplified manner as follows With regard to the preparation of the catalyst 1 Ammonium heptamolybdate reacts with warm hy drochloric acid to form NH4C1 H20 and cis trans cis Mo02Cl2 H0 y This species has been detected in solution 5 isolated as Mo02C12 H20 H20 C2H54NIC1 6 and more recently as the outer sphere diglyme adduct Mo02C1 H20 diglyme 7 Molybdenum trioxide previously dissolved in the mini mum amount of 12 NH3 can be used in place of ammonium molybdate in this preparation 2 DMSO is able to displace H20 from the coordination sphere of many metallic centers producing a more hydropho bic environment around the metal Thus the HCl NHaCl Mo02Ci2 H20 2 aqueous solution reacts with excess DMSO and the resulting cis trans cis Mo02Cl DMSO precipi tates while NH4C remains dissolved With regard to the preparation of OPPhg 1 PPh3 reacts with DMSO in the presence of Mo O2Cl DMSO 2 to give OPPh3 and DMS as repre sented in the catalytic cycle PPh OPPh Mo O CH DMSO Mo OCL DMSO P DMS AA 2 The lack of color in the resulting DMSO solution which con
86. teachers It shows a sample of zinc rod on the left hand side of the page The bottom portion of the rod was etched by human handling this portion of the rod was exposed as the rod was passed around classes over a period of several semesters the top portion of the tod had a protective cover and reveals the boundaries be tween different grains As discussed in the accompanying paper Geselbracht M J Ellis A B Penn R L Lisen sky G C and Stone D S J Chem Educ 1994 71 254 the bubble raft on the right hand side of the cover also shown schematically in Figs 2 and 3 in the paper provides a model for the grains which are close packed arrays of atoms having different relative orientations 23 Intensity 1000 R ol 10 20 30 4 50 60 7 80 90 100 28 degrees Figure 1 X ray powder diffraction pattern of a sample of Y Gd 5Fes0 2 prepared via a mixed metal hydroxide precursor Diffraction peaks that are marked with an asterisk correspond to the impurity AFeO R Y or Gd transformers We believe that a discussion of the chemis try of magnetic solids in introductory chemistry courses not only illustrates the effect of unpaired electrons but also introduces the concept that electrons in a solid can communicate with one another leading to properties that are vastly different from those stemming from isolated lo calized electrons What do we mean by the chemistry of magnetic solids The magnetic p
87. to complete crystallization Note if you do not see solid after 1 h continue to heat and stir until you do sometimes it takes a bit longer Collect the product by vacuum filtration using a B chner funnel Wash out the flask and the crystals on the filter with plenty of deionized water about 3 x 10 mL Allow the product to dry until the next lab period and then weigh the dry final product to determine the yield of dry product 3 C Preparation of Mn acac 3 Add approximately 1 0 g of MnCl 4H20 and 2 6 g of sodium acetate trihydrate into a 100 mL Erlenmeyer flask Add a stirring bar and dissolve the solids in a minimal amount of distilled water add very small amounts at a time until the solids dissolve completely When the solids are dissolved add 4 0 mL of acetylacetone with continued stirring Prepare another solution containing 200 mg of KMnO in 10 mL of deionized water Make sure you stir this for quite a while KMnO is difficult to dissolve and it color makes it hard to see if it has dissolved Add the KMnO solution slowly and drop wise with stirring to the above mixture After addition is complete a small portion of distilled water 1 2 mL should be pipetted using a disposable pipet into the flask or beaker originally containing the KMnO solution and then used to rinse the walls of the reaction flask to remove any permanganate that is sticking to the side After stirring the mixture for about five minutes add drop wise a sec
88. u micas en el laboratorio en t rminos de su significaci n y de las teor as que la sustentan Adquirir destreza en el manejo de las principales t cnicas instrumentales empleadas en qu mica y poder determinar a trav s del trabajo experimental las propiedades estructurales termodin micas y el comportamiento cin tico de los sistemas qu micos En las p ginas siguientes encontrar s instrucciones para sintetizar algunos compuestos de coordinaci n y organomet licos que deber s caracterizar con los medios m s habituales en qu mica No se trata de realizar los experimentos deprisa ni de obtener muy altos rendimientos sino de comprender los principios qu micos asociados a cada experimento No todos los alumnos har n los mismos experimentos con frecuencia distintos alumnos realizar n experimentos complementarios de forma que para discutir algunos resultados necesitar s usar datos o compuestos obtenidos por otros compa eros de laboratorio El trabajo en equipo requiere cuidado y atenci n los resultados de otros dependen de ti A continuaci n de cada gui n se han recogido algunos art culos y fragmentos de libros que te pueden ayudar a realizar los experimentos y a interpretar los resultados as como otra bibliograf a recomendada Lee este material adicional atentamente antes de realizar los experimentos Tu profesor te instruir en el manejo de aquellos instrumentos disponibles para la caracterizaci n estructural y te dar l
89. ubsequent reoxidation with air the cobalt II salts are air sensitive but can be isolated and their properties studied yields a complex which retains its chirality In fact reduc tion reoxidation of the Co diamsarH3 5 E1 2 0 18 V or Co diamsar 3 E1 2 0 54 V versus SCE product can be performed at room temperature with total retention of ligation and chirality the same experiment performed with chiral Co en 3 leads to complete loss of chirality This is a simple test of the unusual stability of the cobalt II macrobicycles which arises as a consequence of the encapsulation of the metal ion within the ligand cavity E m WERFEN 4 3 ppm Figure 2 H NMR spectrum in D20 N deuterated of Co dinosar Volume 62 Number 9 September 1985 805 4 Krause R A and Magargle E A J CHEM EDUC 53 667 1976 5 Curtis N F Coord Chem Rev 3 3 1968 Lindoy L F and Busch D H Preparative Inorg React 6 1 1971 ya 6 Sargeson A M Chem Brit 15 23 1979 o Tea G ae H Practical Inorganic Chemistry 2nd ed Chapman and Hall 7 Harrowfield J MacB Herlt A J and Sargeson A M Inorg Synth 20 85 1980 ndon 2 8 Bond A M Lawrance G A Lay P A and Sargeson A M Inorg Chem 22 2010 2 ke an Synthesis and Technique in Inorganic Chemistry W B Saunders Co 1983 iladelphia 1969 9 Geve R J Hambley T W Harrowfield J MacB Sargeson A M and S
90. ut solid so lutions and the tunability of properties by varying the composition of a solid solution Furthermore it can be per formed in such a way that each student has a unique com pound to prepare The class data can then be compiled to obtain a picture of the magnetic properties of the entire range of composition of Y Gdy FesOyz The majority of molecules and solids that we encounter are nonmagnetic All of the electrons in these materials are paired and the molecule or solid is said to be diamagnetic The simplest type of magnetism paramagnetism often is demonstrated in introductory chemistry courses by observ ing the behavior of liquid oxygen in a magnetic field Due to the presence of unpaired electrons in Oz the liquid is Author to whom correspondence should be addressed 696 Journal of Chemical Education attracted to a strong magnet and if a large horseshoe mag net is used the liquid oxygen appears to hover trapped between the poles of the magnet 1 Many solids exhibit interesting magnetic behavior as well often more complex than simple paramagnetism due to the cooperative effect of many electrons in the solid act ing in concert Ferromagnetism is a property of solids that is technologically important and exploited in the use of permanent magnets magnetic recording media and Addendum Description of the March 1994 Cover The cover of the March 1994 issue needs further ampli fication to be useful for
91. y en B se colocan 20 g de NaCl cubiertos de cido clorh drico concentrado El tubo de ensayo D debe contener el complejo de n quel que se pretende destruir Cuestiones 1 Indicar la geometr a de todos los compuestos de n quel y cobre empleados como reactivos y obtenidos como productos 2 Porqu es necesario a adir una disoluci n de HCl en el matraz B para generar HCl 3 Se usa una sal am nica para separar el macrociclo de la sal de n quel Podr a usarse una sal pot sica Razonar la respuesta References 1 Lindoy L F The Chemistry of Macrocyclic Ligand Complexes Cambridge University Press Cambridge 1989 2 Sacconi L Mani F Bencini A In Comprehensive Coordination Chemistry Wilkinson G Gillard R D McCleverty J A Eds Pergamon Press Oxford 1987 Vol 5 Chapter 5 Sect 50 5 9 3 Merrell P H Urbach F L Arnold M J Chem Educ 1977 54 580 582 4 Goedken V L Weiss M C Place D Dabrowiak J Inorg Synth 1980 20 115 119 5 Tait A M Busch D H Curtis N F Inorg Synth 1978 18 2 9 49 8 Woodruff W H Pastor R W Dabrowiak J C J Am Chem Soc 1976 98 7999 8006 50 7 B S ntesis de un complejo encapsulado de cobalto En este experimento el metal dirige la reactividad de los ligandos para formar un biciclo que act a como ligando criptando en torno a l Ly en Figura 2 Figura 2 Procedimiento experimental Co
92. ygen atom transfer reactions involving dioxomolybde num VI complexes are of current interest because of their relevance in some important biological processes 1 Most synthetic complexes that mimic oxotransferases contain sterically demanding sulfur ligands because two of the cri teria for relevant models are the sulfur environment and hindrance to irreversible u oxo dimer formation However some molybdenum complexes Jacking these requisites show a remarkable ability to act as oxotransfer agents 2 Here we describe the facile synthesis of a simple very active catalyst Mo0 Ck DMSO DMSO dimethylsulfoxide and its application in the oxidation of triphenylphosphine PPhg to triphenylphosphine oxide OPPha by DMSO This oxidation of PPh3 provides a good example of the catalytic exotransfer process because PPh3 is inexpensive resistant to aerial oxidation widely used in oxotransfer studies and has a low volatility Conducting the experi ment in an aprotic medium with simple reagents mini mizes the number of species involved in the overall proc ess which facilitates the interpretation of the results at the time that dramatically evidences the role of the cata lyst cleavage of strong multiple X O bonds Preparing the Catalyst The procedure presented here is related to that recently reported for the multigram scale synthesis of MoO2Clg DMSO from aqueous hydrochloric solutions af MoO 3 although the use of NH 46Mo0702

Download Pdf Manuals

Related Search

Related Contents

Feiyue FY811 User's Manual  ECSTRA VERDE  HD3000 - Optoma  

Copyright © All rights reserved. Failed to retrieve file