HINGE DISTORTION IN PLATINUM(II) DIMERS WITH A PT2S2 RING - AN AB-INITIO MOLECULAR-ORBITAL STUDY

Ab initio calculations have been carried out for Pt(II) dimers with S2 - and/or RS(-) bridging ligands in order to elucidate the factors gove rning the structural preference, planar or hinged, of these complexes. Calculations have been performed for systems which model all structur ally characterized Pt(II) binuclear complexes. All possible determinan ts of the hinge angle have been taken into account in the ab initio ca lculations. These show that electronic rather than steric effects gove rn the geometry of the central Pt2S2 ring. Only one minimum of energy has been found for each complex, but the energetic cost of the hinge m otion is low. Complexes with two S2-, or with one S2- and one RS(-), b ridging ligands are hinged; the decrease of the through-ring antibondi ng interaction between the in-plane sulfur p orbitals with folding app ears to be the determinant for hinging. Complexes with two RS(-) bridg ing ligands can be planar or hinged depending on the relative orientat ion, syn or anti, of-the R groups, on the nature, L(4) or L(2)L(2)', o f the terminal ligands, and in the latter case on their disposition, c is or trans. However, the aromatic or aliphatic nature of bridging thi olates does not influence the geometry of the Pt2S2 ring significantly . Conclusions drawn from platinum dimers can be extended to the pallad ium analogs.