Structural correlations and conformational preference in edge-sharing binuclear d8 complexes with XR2 bridges.: A theoretical study

The binuclear complexes of d(8) transition metal ions of the type [M-2(mu-XR2)(2)L-4] (where M = Rh-I, Ir-I, Ni-II, Pd-II, Pt-II, or Au-III; X = S, N, P, or As) appear in a variety of molecular conformations in which the coordination planes around the two metal atoms are sometimes coplanar, sometimes bent. For the bent compounds with asymmetric bridges, (XRR2)-R-1, the substituents adopt different orientations relative to the metal framework and to each other. Ab initio theoretical studies on the different conformers of 30 representative complexes, complemented with a structural database analysis, have allowed the establishment of structural correlations in this family of compounds. The conformational choice results from a delicate balance of different interactions which are qualitatively analyzed, such as the changes in bond angles around the bridging atoms, the existence of weak metal...metal bonding in the bent structures, and steric interactions involving the terminal ligands and the substituents at the bridging atoms.