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

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.