Octahedral symmetry, effect orbital configuration

A Jahn-Teller distortion should also occur for configuration d. However, in this case the occupied orbital is a t g orbital, for example d, this exerts a repulsion on the ligands on the axes x and y which is only slightly larger than the force exerted along the z axis. The distorting force is usually not sufficient to produce a perceptible effect. Ions like TiF or MoClg show no detectable deviation from octahedral symmetry. 

In octahedral symmetry, the copper(ll) ion has a electronic ground state due to the d electron configuration with the unpaired electron in an Cg a anti-bonding orbital. An exact octahedral geometry of six-coordinate copper(II) complexes is never realized due to a strong Jahn-Teller effect. The symmetry of the Jahn-Teller active vibration is eg, the non-totally symmetric part of the symmetric square [Eg Eg]. For a Cu(Il)Lg complex, the two components of the degenerate eg vibration are shown in Fig. 1 a [2]. 

An S term, like an s orbital, is non-degenerate. Therefore, while the effect of a crystal field (of any symmetry) will be to shift its energy, there can be no question of its splitting. The ground term for the configuration is S. In an octahedral crystal field, this is relabelled Aig, in tetrahedral symmetry, lacking a centre of inversion, it is labelled M]. 

The compound Cr2As should have the charge configuration Cr Oi As3-. Since the octahedral interstices have tetragonal (c/a >1) symmetry, the single eg electron at a Cru occupies a dti orbital oriented parallel to the c axis. This ordering increases the axial ratio (Jahn-Teller effect). With c/a 1.76, R2 = 2.53 A < =... 

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