Complexes with sulphur and selenium donor ligands. Part III. The electronic spectrum of bis(dimethyl phosphorodithioato)-2,9-dimethyl-phenanthrolinenickel(II)

Abstract

The crystal polarised electronic spectrum of the title compound has been recorded at room temperature and at liquid-helium temperature in three orthogonal directions. From the observed polarisations of the absorption bands, a ground state ³B₂ has been deduced in an effective symmetry C_2v. This inversion in ground state from that previously found for trigonal bipyramidal C_2v symmetry is ascribed to the very large (z-axis) SNiN angles, i.e. the small ‘bite’ angle of the phenanthroline ligand.

From a total of eleven bands observed at 4·2 K, three are assigned to spin-forbidden transitions, and the energy order, ³B₁(³E″) < ³A₂(³E″) < ³B₁(³A₂″) < ³A₂(³A₁) < ³B₂(³A_a′) < ³B₁(³E″) < ³B₂(³A₂′) < ³A₂(³E″), suggested for the other eight (parent D_3h terms in parentheses). The transition within the split level ³E′(D_3h) could not be located.

The energies of the bands in solid-state electronic spectra are similar to those in acetone solution, indicating predominant existence of the same five-co-ordinate species in solution.