Chromium complexes electronic spectra

Malonic acid CH2(C02H)2 (H2mal) (209) has a coordination chemistry with chrommm(III) closely resembling that of oxalate. Malonic acid is a slightly weaker acid than oxalic acid and slightly more labile complexes are formed. The tris complex is the most extensively studied, prepared by the reduction of chromate solutions or the reaction of chromium(III) hydroxide with malonate.917,918 919 The cis and trans diaqua complexes may be prepared by the reduction of chromate with malonate the isomers are separated by fractional crystallization. The electronic spectrum of the tris complex is similar to that of the tris oxalate and a detailed analysis of these spectra has appeared.889... 

The complex [Cr(DMF)6][Cl04]3 has been prepared from the reaction of chromium(III) perchlorate with DMF (90 °C, 10 h).951 Solvent exchange and substitution proceed by h mechanisms.947,952 The complex [Cr(DMF)6]Br3-DMF was prepared by the reaction of chromium metal with bromine in DMF 953 the electronic spectrum of this complex was very similar to that of the perchlorate salt. 

A new method1006 is the oxidative decarbonylation of Cr(CO)6 with [Hg(S2CNEt2)2] in 2 3 molar ratio to give the chromium(II) complex followed by aerial oxidation of the reaction mixture (Scheme 101). Although the unoxidized intermediate solution has the electronic spectrum of the chromium(II) complex (Section 35.3.6.1) the reaction pathway is not completely clear. 

At - 78°C, the one-electron oxidation of the acyl complexes [M(COR)(CO)5]" (M = Cr or W, R = alkyl or aryl) is quasi-reversible the lifetime of [Cr(COPh)(CO)5] is 20 msec. The ESR spectrum of the chromium complex is similar to that of the benzaldehyde anion, shows no metal hyperfine coupling, and suggests the unpaired electron to be largely based on the acyl ligand. 

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."... 

Study of the phosphorescence (and absorption) spectra of chromium(III) complexes has been used to determine to what extent delocalization of metal d electrons onto the ligands is possible. Using the absorption spectrum of Cr(H20)83 +, for example, it is possible to... 

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