Tetragonal elongation

The particular values and power dependence for the d-s mixing term are also not too critical although a certain threshold must be achieved. Tetragonally elongated Jahn-Teller distortions of d9 CuNe species (36) and the trigonal geometry of the oxidized copper center in Type 1 metalloproteins (37) can be achieved with an inverse sixth order power dependence and an associated a6 parameter of at least 300,000 kcal mol-1 A6. However, since eds also depends on symmetry—e.g., it makes no contribution for octahedral complexes—there are many systems where d-s mixing has a minimal effect. 

Fig. 12. Schematic energy level diagram illustrating the Jahn-Teller stabilization energy accompanying a tetragonal elongation of an octahedral Cu(II) complex.

Elongated tetragonal Compressed tetragonal Elongated rhombic Compressed rhombic ... 

Tetragonally compressed Octahedral Tetragonally elongated Square planar ... 

Fig. 1. The splitting of the d orbitals in tetragonally compressed, tetragonally elongated, and square planar geometric for a d1 ion and the resulting relative g values for d7 and d9 configurations.

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