Complexes with sulphur and selenium donor ligands. Part II. Crystal spectra of some tris(bidentate ligand)–metal(III) complexes

Abstract

The polarised single-crystal spectra of some tris-(OO′-diethyl phosphorodithioato)- and tris(diethyldithiocarbamato)-metal(III) complexes have been recorded. All show extensive splitting of the parent terms in O_h symmetry arising from the trigonal distortions present, and the polarisation behaviour of the bands may be interpreted in terms of a D₃ symmetry about the metal ion. Assignments have been made for Co³⁺, Cr³⁺, Rh³⁺, and Ir³⁺ in this symmetry. Furthermore, it is found that the A-term lies lower in energy than the E-term (both terms being derived from the parent T-term in O_h symmetry) for all the complexes examined. A point-charge calculation, with both the angle subtended at the metal by the bidentate ligands (the ‘trigonal’ angle) and also the angle of tilt of each of the ligands to the C₃ axis being varied, was performed in order to rationalise this energy order. The calculation does predict this energy order for a trigonal angle of <90°, and shows that changes in the angle of tilt of the ligands from the C₃ axis cause little effect in the energy-level order; the order predicted for a given ‘trigonal’ angle is critically dependent on the ratio of the radial integrals, the experimental results indicating a value for the latter of 〈R₂(r)〉/〈R₄(r)〉 of ca. 0·9.