Bonding and conformational aspects of thiolato-bridged early-late heterobimetallics

Extended Huckel and Fenske-Hall MO calculations have been used to examine the bonding in a series of thiolato-bridged early-late heterobimetallics. The calculations support the postulate of a weak, dative interaction between the electron-rich late metal and the electron-deficient early metal center. Generally, for Ti species the interaction is weak σ bonding in character, although for Zr there is an indication of an additional π component. When the coordination sphere of the late metal center is trigonal or square planar, these interactions result in a MS₂M′ core folding and an endo-cisoid conformation of the substituents on the bridging S atoms is adopted. Alternatively, a endo-transoid conformation and a planar MS₂M′ core is seen when the late metal center requires a pseudotetrahedral coordination geometry. The implications of these results with respect to the structural and electrochemical properties is considered.