A pseudo-Jahn-Teller effect, coupled with the E(X) epsilon Jahn-Teller effect

Abstract
The authors show under what conditions a pseudo-Jahn-Teller effect, for which odd distortion modes are active, can couple with the E(X) epsilon Jahn-Teller effect, which arises for certain transition-metal ions in octahedral and tetrahedral arrangements of ligands. The geometries of CuCl6 octahedra as found in CsCuCl3 and (CH3)4NCuCl3 at room temperature, which show this pseudo-Jahn-Teller effect, are discussed.