The Jahn-Teller Effect of Cu2+ in Six-, Five- and Four-Coordination — Examples for the Importance of Vibronic Interactions in Transition Metal Chemistry

Abstract

The stereochemistry of transition metal ions in high symmetry ligand fields is frequently determined by strong vibronic interactions between the electronic groundstate and certain nuclear motions, often leading to pronounced distortions of the environment as well as large term splittings and energetic groundstate lowering effects. These distortions may be of “dynamic” or “static” nature, depending on the ratio between the thermal energy and the vibronic interaction energies, which determine the minima in the groundstate potential surface. A prominent example is Cu2+, which undergoes very pronounced and moderately strong vibronic couplings of the Jahn-Teller type in octahedral (E ⊗ e) and tetrahedral coordination (T2 ⊗ e), respectively, but also exhibits rather strong vibronic interactions between groundstate and the first excited in trigonal-bipyramidal coordination (A’ ⊗ e’ ⊗ E’: “pseudo-Jahn-Teller effect”).