Jahn-Teller effect in high spin d4 and d9 octahedral metal-complexes

Abstract

The Jahn-Teller effect, which is the geometrical effect on a molecule due to the energy lowering of spatially degenerate electronic ground states, is not determined, as is often perceived, by the shape of the highest occupied molecular orbital (HOMO), or the shape of a singly occupied molecular orbital (SOMO), but is determined rather by the difference in concentration of electron density (before distortion) between the metal and the two ligands on the z-axis, and concentration of electron density between the metal and the four ligands lying in the xy-plane. A higher concentration of electron density between the metal and the two ligands on the z-axis, than between the metal and the four ligands on the xy-plane, will lead to elongation (z-out) Jahn-Teller distortion. Accordingly, high spin, S = 2, d4 octahedral metal-complexes with a dz2 HOMO, as well as S = ½, d9 octahedral metal-complexes with a dx2-y2 HOMO, both exhibit elongation (z-out) Jahn-Teller distortion.