Diphosphane derivatives. Part 3. The donor characteristics of tetramethyl-1,2-dithioxodi-λ5-phosphane (tetramethyldiphosphine disulphide) and the vibrational spectra and structures of some of its complexes

Abstract

The i.r. spectra of tetrahedral [M(P₂Me₄S₂)₂]²⁺, pseudo-tetrahedral MX₂·P₂Me₄S₂, and cis-octahedral MX₄·P₂Me₄S complexes of tetramethyl-1, 2-dithioxodi-λ⁵-phosphane (tetramethyldiphosphine disulphide), P₂Me₄S₂(X = halide), are all consistent, in the region of the ligand skeletal stretching frequencies, with D_2d or C_2v symmetry for the complex species and with a planar cis-chelate configuration for the co-ordinated P₂Me₄S₂ ligand. Comparisons with the spectra of (CuCl ·P₂Me₄S₂)₂, which contains gauche-chelate P₂Me₄S₂, and with (CuCl₂·P₂Me₄S₂)_n, in which the ligands retain the internal trans conformation, indicate that the trans ligand may be identified by the absence or relative weakness of the P–P and symmetric P–S stretching absorptions, but the vibrational data alone cannot distinguish reliably between the cis- and gauche-chelate structures. The ligand-field parameters 10Dq and β measured for P₂Me₄S₂ in the [Co(P₂Me₄S₂)₂]²⁺ ion both appear to be significantly higher than the corresponding values for unidentate PMe₃S in [Co(PMe₃S)₄]²⁺.