PSEUDO SECOND-ORDER JAHN-TELLER EFFECTS AND SYMMETRY CONSIDERATIONS IN TRANSITION METAL POLYHYDRIDE COMPLEXES

摘要

Pseudo second-order Jahn-Teller distortions are proposed to explain why the equatorial hydride ligands in a series of cyclopentadienyl metal polyhydrides (Cp*ReH6, Cp*OsH5, Cp*IrH4) bend away from the Cp ring at such large angles. Restricted Hartree-Fock (RHF) geometry optimizations on models of these complexes where the Cp* ring has been replaced by a hydride reproduce these large distortions. Walsh diagrams and Mulliken populations have been used to show that the stability provided by distortion results from maximizing the overlap population between the hydride s orbitals and the metal d orbitals. This study also includes a comparison of previous work on the structures of d(0) MH6 complexes with our work on d(2) MH6 complexes. We found that an occupied d orbital has a significant effect on the geometry of this type of molecule due to the change in hybridization on the metal from sd(5) to spd(4). Symmetry arguments are demonstrated as a means to predict the low energy geometries of these complexes. [References: 28]