Indium(III) halide complexes with trimethylphosphine sulphide and trimethylarsine sulphide: structures and bonding of [InX3(Me3MS)2](X = Cl or Br, M = P or As) and [InCl3(H2O)(Me3AsS)2]

Abstract

The crystal structures of four isomorphous compounds [InX₃(Me₃MS)₂], with X = Cl or Br and M = P or As, and of a related octahedral complex [InCl₃(H₂O)(Me₃AsS)₂] are described. In the isomorphous series, the indium is in a distorted trigonal-bipyramidal co-ordination with the thio ligands in apical positions. The distortions, which include small differences in the lengths of the two In–S bonds in each molecule, are produced by a combination of intra- and inter-molecular repulsions. The average In–S bond lengths for each molecule show qualitative decrease with the increasing charge transfer to be inferred from ligand polarity and halogen electronegativity. Comparison with bond lengths in the octahedral complex [InCl₃(H₂O)(Me₃AsS)₂] shows the characteristic lengthening of the apical trigonal-bipyramidal bonds. The M–S bonds of the ligands show the usual lengthening upon co-ordination, with a moderate fall in bond order, e.g. from 2.0 to 1.6 in [InCl₃(Me₃PS)₂]. ³¹P N.m.r. spectra also point to a reduction in the π character of the P–S bonds. There is no evidence for the use of In d orbitals in the In–S bond.