Far-infrared studies of metal-ligand vibrations.

A study is made of the infrared absorption frequencies associated with metal-sulphur bonds. Variations of the metal-sulphur stretching frequency, [v (m-s)], with metal, oxidation state, coordination number, and configuration are discussed. The monodentate ligands used are thiourea and ethylene-thiourea, and from the results assignments are made of the previously reported far-infrared spectra of some thiocyanato-complexes. A range of dithietene complexes and complexes of 0-0' diethyldithiophosphate are investigated to observe the effect on v (m-s) of using chelating-ligands. v (m-S) has been found for thiourea and ethylene-thiourea complexes in the range 298-205 cm-1, although lead complexes can have v(m-s) at least as low as 160 cm-1 . For thiocyanato complexes a narrower range from 314-280 cm -1 has been defined. No definite correlations can be made for the bidentate ligands, although one or more bands attributable to v (m-s) are present between 436-288 cm-1 in dithietene complexes, and betweem 330-220 cm-1 in dithiophosphate complexes. Metal-metal bond stretching frequencies in the Raman and far-infrared are reported for a series of carbonyl and cyclopentadienyl carbonyl complexes. Since both the symmetric and antisymmetric stretches have been observed in some cases it has been possible to evaluate both the bond stretching force constant and the stretch-stretch interaction force constant. The interaction constants are surprisingly high compared with the bond stretching constants. The far-infrared spectra of the alpha- and beta-forms of both rhodium trichloride and ruthenium trichloride are reported and the structural implications discussed.