Degenerate systems, distortion

A Copper(II) is a Jahn-Teller ion and normally sits in a distorted lattice site. The configuration of copper is which leads to an unpaired electron in the e level in an octahedral crystal field. The Cg level consists of the degenerate and d, orbitals. According to the Jahn-Teller theorem, the system distorts to remove the degeneracy and lower the overall energy of the system. Hence one set of bonds (four in plane, or two axial) become longer than the others and the copper ion has a distorted geometry. 

In relation to the above, a brief account will be given here of the Jahn-Teller effect.When the electronic level of a molecule is degenerate at a structure of high symmetry, this structure is generally unstable and nuclear displacement may remove the degeneracy to stabilize the system. Distortion due to the effect will take place as the result of the terms of the vibrational Hamiltonian linear in the normal coordinates. 

Vibrational stmcture is, at best, only partially resolved. The stmcture in the first and second systems is complex which could be due, in part, to there being a Jahn-Teller effect in each of them. Such an effect may arise when a molecule is in an orbitally degenerate E (or T) state. The Jahn-Teller effect involves a distortion of the molecule in order to destroy the... 

For these latter systems, the effects of static distortions have been considered for a separation, A, of the erstwhile degenerate components of the n or 5 levels, in the absence of spin-orbit coupling, and expressions for the g values are readily derived (68, 72,101). 

Oddershede s calculations were limited by the computational facilities and more recent calculations indicate that while Manne s ordering of the occupied molecular orbitals stays unchallenged, there is little significance to assign to virtual orbitals for an anion [6]. It was pointed out [5] that ionization from a degenerate state would lead to a distortion in the system due to the Jahn-Teller theorem. 

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