Chromium compounds, spectra

The cyclopentadienyl chromium compound, an open sandwich structure, has a spectrum about as devoid of fine structure as one might expect of a... 

Comparison of the electrical conductivities of chromium penta-phenyl hydroxide, sodium hydroxide and ammonia in absolute methyl alcohol and in methyl alcohol-water solution, shows that the former is a very strong base. In aqueous methyl alcohol solution the chromium compound does not appear to approach the limiting value with increasing dilution. The ultra-violet absorption spectrum examined in absolute ethyl alcohol solution resembles that of chromic acid and the dichromates, but the absorption is noticeably greater in the case of the organic compound. 

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. 

The spectrum of the organometallic compound dimesitylene chromium, [C Hj(CHs)3]2Cr, has relatively high amplitude. The location of the principal peak, 18 ev., corresponds to that of divalent chromium. 

Figure 20 contains spectra of compounds in which the chromium is of nominal valence - -6 and is tetrahedrally coordinated. The chromate ion shows a type IV spectrum extending out to about 100 ev. which is inde-... 

It is worthy of note that in the complexes with Csv symmetry such as [CuBr(Meetren)]Br (47, 42) (Fig. 10) the spectra still have two d—d bands and have much the same appearance as those of Dsh chromophores (Fig. 14). In the above compound the two bands, when resolved into Gaussian components, are found at 10.3 (e 450, P = 5.4-10 3) and 13.5 kK (e 180, P=1.4-10 3) ( ). Their separation of 3.2 kK is in this case too large to be attributed solely to spin-orbit couphng and the two bands are therefore assigned as - 2 (1) and - 2 (2) (8). This spectrum is very similar to that of the chromium(II) analog (d< configuration). 

Pentacarbonyl(l-oxacyclopent-2-ylidene)chromium(0) is an air-stable, bright yellow compound that dissolves readily in most organic solvents. The infrared spectrum of a heptane solution shows bands at 2066 (s), 1983 (m), 1958 (s), and 1944 (s) cm"1. The proton NMR spectrum in CS2 shows a two-proton triplet (7 = 8 Hz) at 6 4.90, a two-proton triplet (7=8 Hz) at 6 3.67, and a two-proton quintet (7=8 Hz) at 6 1.96 all relative to internal tetramethylsilane. 

The intermediate cyclooctene complex appears to be more reactive with respect to CS coordination and more sensitive to oxidation when the arene ring bears electron-withdrawing groups (e.g., C02CH3). Dicarbonyl(methyl rj6-benzoate)-thiocarbonyl)chromium is air stable in the solid state and reasonably stable in solution.9 The infrared spectrum exhibits metal carbonyl absorptions at 1980 and 1935 cm"1 and a metal thiocarbonyl stretch at 1215 cm"1 (Nujol) (these occur at 1978, 1932, and 1912 cm"1 in CH2C12 solution).10 Irradiation of the compound in the presence of phosphite or phosphine leads to slow substitution of CO by these ligands, whereas the CS ligand remains inert to substitution. The crystal structure has been published."... 

A coordination number of 7 does not seem likely for chromium (III) also, the infrared spectrum indicates that this compound contains uncoordinated hydroxyl groups. The similarity of the visible-ultraviolet absorption spectra of [Cr(HO-A)2] and [Cr(AcO-A)2] (above) is further evidence of the identical character of the donor groups in both compounds, and hence, hydroxyl groups appear to be uncoordinated in the former. We must seek an explanation not involving coordination of the hydroxyl oxygen to chromium (III). 

The mass spectra of binuclear cyclopentadienylmetal carbonyl derivatives of chromium and molybdenum provide useful indications of the relative strengths of the metal-metal bonds in various compound types. The mass spectrum of [C5H5Cr(CO)3]2 (S. M = Cr) exhibits no bimetallic ions but only monometallic ions such as CsHsC CO) (n = 3,... 

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