Structural variation in diorganotin dimethylxanthates, R(2)Sn(S(2)COMe)(2): A combined crystallographic and theoretical investigation

The crystal and molecular structures of three R₂Sn(S₂COMe)₂ compounds have been determined and show that the tin atom in each case exists in a distorted trapezoidal bipyramidal geometry with the tin-bound organo substituents lying over the longer edge of the trapezoidal plane. For Me₂Sn(S₂COMe)₂, one of the xanthate ligands coordinates via both sulfur atoms (S-,S- chelation) but the other uses one sulfur and the oxygen atom in coordination to tin (S-,O- chelation). More conventional geometries, with S-,S- chelation only, are found for Ph(Me)Sn(S₂COMe)₂ and Ph₂Sn(S₂COMe)₂. Theoretical predictions of the isolated molecular structures have been calculated using ab initio and density functional theories (all with the 3-21G** basis set) and reveal a different arrangement of the ligand donor set for each compound, i.e., one featuring both ligands with S-,O- chelation. Differences between the single-molecule and solid-state structures are ascribed to the influence of intermolecular interactions on the molecular geometries in the solid state