Secondary bonding. Part 15. Influence of lone pairs on co-ordination: comparison of diphenyl-tin(IV) and -tellurium(IV) carboxylates and dithiocarbamates

Abstract

Seven complexes of general type Ph₂MX₂ with X = carboxylate or dithiocarbamate have been prepared and their molecular structures determined (M = Sn, X = O₂CMe, O₂CCH₂Cl, or S₂CNEt₂; M = Te, X = O₂CCCl₃, S₂CNEt₂, S₂CNEtPh, or S₂CNPh₂). All but one show unsymmetrical bidentate co-ordination by the carboxylate or dithiocarbamate ligands; the tellurium complexes show substantially greater differences between the longer and shorter M–O or M–S distances. The presence of the lone pair transforms the co-ordination geometry from approximately tetrahedral (M = Sn) to pseudo-trigonal bipyramidal (M = Te). Replacing carboxylate by dithiocarbamate has a modest effect when M = Te, but in the tin compound the sulfur ligand co-ordination is almost symmetrical. This contrasts with the unsymmetrical bonding in Me₂Sn(S₂CNEt₂)₂.