Charge-transfer transitions metal-carbonyl complexes

The d-d transitions in most of the d6 metal carbonyls and cyanides are hard to locate with certainty, since the large A-values mean that metal-to-ligand charge transfer may occur at about the same energy as the two bands due to the tagf -) - eg(cr ) transition. For the complexes in which the metal furnishes fewer than 6 valence electrons (such as the d6 Fe(CN)e3 ), additional charge-transfer bands due to ligand-to-metal transitions further obscure the weak d-d bands.8 Nevertheless, in many cases reliable values for A are available for M(CO) and M(CN)6n complexes. These A-vahies are summarized in Tahle III. 

A simple view of the mode of bonding of the carbon monoxide molecule to the surfaces of the transition metals and in their carbonyl complexes is well known and is thoroughly described in the literature.4 These metals have unfilled d-orbitals (or holes in their d-band), and the molecule in the linear form is held by a push-pull bond in which charge is transferred from the 5a orbital of the molecule into the metal s d-band, while there is back-donation of charge from the top of the d-band into the molecule s vacant... 

Diorgano ditellurium compounds react with transition metal salts and carbonyl complexes to form coordination compounds (Table 5, p. 283). Complexes with the following transition metals have been reported Ti, Cr, Mo, W, Mn, Re, Fe, Ir, Ni, Pd, Pt, Cu, Ag, Cd, Hg, Yb, and U. In many of these complexes, the organyltelluro group bridges the metal atoms in binuclear complexes. The Te —Te bond seems to remain intact upon complexation to mercury halides, rhenium carbonyls, and uranium pentachloride. For details on tellurolatO bridged complexes see p. 212. Complexes with SnCl are also known. Diphenyl ditellurium and bis[4-ethoxyphenyl] ditellurium formed charge-transfer complexes when equimolar amounts of the ditellurium compound and tetracyano-p-quinodime-thane were refluxed in acetonitrile. ... 

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