Cobalt compounds, spectra

Reaction of HCofPfOPh), with PMMA. A 1.0g sample of PMMA and 1.0g of the cobalt compound were combined as above. After pyrolysis at 375°C for two hours the tube is noted to contain char extending over the length of the tube with a small amount of liquid present. The gases were found to contain CO, C02, hydrocarbon (probably methane), and 0.1 Og methyl methacrylate. Upon addition of acetone, 1.0g of soluble material and 0.19g of insoluble may be recovered. The infrared spectrum of the insoluble fraction is typical of char. 

The spectrum of sodium cobaltinitrite shown in Fig. 13 is also of type I with the maximum at 27 ev. The spectrum differs from the ammonia and ethylene diamine coordinated cobaltic compounds in yielding a pattern... 

Spectra of a variety of chromium compoimds in the +3 valence state are included in Fig. 16. The principal peak is centered at about 22-25 ev. in all cases. The CrjOa spectrum is almost identical to that of Mn02 of Fig. 5. Spectra of the oxalato complex and the ammonia complex are almost identical to spectra of the corresponding cobalt compounds of Figs. 13 and 11. 

Figure 6.18 illustrates the technique with a study on a proprietary cobalt on alumina Tropsch catalyst for Fischer-Tropsch synthesis (the reaction of synthesis gas, CO + Fl2, to hydrocarbon fuels) [55]. Trace amounts of platinum help to obtain an appreciable degree of reduction for the cobalt (similarly as in the temperature-programmed reduction of bimetallic Fe-Rh catalysts in Fig. 2.4). The left part of Figure 6.18 shows Co K-edge XANES of metal and oxide reference compounds, and illustrates the strong intensity of the white line region for ionic cobalt compounds. The XANES spectrum of the calcined CoPt/A Ch catalyst re-...

Nuclear magnetic resonance studies on spin labeled derivatives are not extremely useful due to the paramagnetism of the molecule. However, the NMR spectrum of spin labeled methylcobinamide confirms that the nitroxyl function is coordinated to the cobalt. It is possible in this compound to obtain good resolution of the methyl group resonance. 

The most direct information on the state of cobalt has come from Mossbauer spectroscopy, applied in the emission mode. As explained in Chapter 5, such experiments are done with catalysts that contain the radioactive isotope 57Co as the source and a moving single-line absorber. Great advantages of this method are that the Co-Mo catalyst can be investigated under in situ conditions and the spectrum of cobalt can be correlated to the activity of the catalyst. One needs to be careful, however, because the Mossbauer spectrum one obtains is strictly speaking not that of cobalt, but that of its decay product, iron. The safest way to go is therefore to compare the spectra of the Co-Mo catalysts with those of model compounds for which the state of cobalt is known. This was the approach taken... 

Although three early papers briefly discussed reactions between methylcobalamin and mercury compounds (30-32), the most systematic investigation has come from Wood and co-workers (33). They proposed the mechanism shown in Fig. 1, with values for the various rate constants presented in Table I. Species 2 and 3, in which the benzimidazole nitrogen no longer bonds to the cobalt atom, are termed base-off compounds, whereas 1 is base-on methylcobalamin and 4 is aquocob(III)alamin, the usual product of aqueous transmethylation by 1. Each one of these species has a unique ultraviolet-visible spectrum, which allows quantitative studies by spectrophotometric techniques to be made (28, 32, 33). The mercuric acetate-1 exchange is so rapid that it must be studied using stopped-flow kinetic techniques (33). 

The products isolated from reactions of amides with transition metal halides usually contain coordinated halide (e.g. the formulations in Table 2). In some cases such as [Co(NMF)6][CoCLt], halide and amide are coordinated to different metal atoms, but when such compounds are dissolved in the neat ligand, halide can be replaced and at high dilution all the metal ions may be fully coordinated by the amide alone. The electronic spectrum resulting when this cobalt complex is dissolved in nitromethane has been interpreted as relating solely to the tetrahedral complex [CoC12(NMF)2]. 

Preparation of (1,2-B9C2H,, )2Co has also been accomplished by the aqueous route. The neutral complex, C5H5Co(l,2-B9C2H,) was obtained in low yield by reaction of an equimolar mixture of C5H5 and 1,2-B9C2Hn2 with cobalt(II) chloride. The proton NMR spectrum of this compound is consistent with a sandwich-bonded structure similar to the iron analog (see Fig. 5). 

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