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The Jahn–Teller effect is responsible for the tetragonal distortion of the hexaaquacopper(II) complex ion, [Cu(OH 2) 6] 2+, which might otherwise possess regular octahedral geometry. The two axial Cu−O distances are 238 pm, whereas the four equatorial Cu−O distances are ~195 pm.
The pyramidalization and energies of inversion of group 15 :MR 3 (M = N, P, As, Sb, Bi) and group 14 •MR 3 molecules can also be predicted and rationalized using a second-order Jahn-Teller distortion treatment. The “parent” planar molecule possessing D 3h symmetry has frontier orbitals of a 2 ” (HOMO) and a 1 ’ (LUMO) symmetries
In their early 1957 paper on what is now called pseudo Jahn–Teller effect (PJTE), Öpik and Pryce [2] showed that a small splitting of the degenerate electronic term does not necessarily remove the instability and distortion of a polyatomic system induced by the Jahn–Teller effect (JTE), provided that the splitting is sufficiently small (the two split states remain "pseudo degenerate ...
For a free ion, e.g. gaseous Ni 2+ or Mo 0, the energy of the d-orbitals are equal in energy; that is, they are "degenerate". In an octahedral complex, this degeneracy is lifted. The energy of the d z 2 and d x 2 −y 2, the so-called e g set, which are aimed directly at the ligands are destabilized.
File:Cu water.png shows the structure of Cu 2+ in aqueous solution, whereas File:Hexaaquacopper(II)-3D-balls.png shows the structure of [Cu(OH 2) 6] 2+ in various crystalline environments. I imagine the editor who originally added the [Cu(OH 2 ) 5 ] 2+ image wanted to point out that the Jahn-Teller-distorted [Cu(OH 2 ) 6 ] 2+ ion is not ...
The tetrahedral point group lacks the inversion operation, so the Laporte rule does not apply. [6] Illustrative of this effect are the disparate extinction coefficients for octahedral vs tetrahedral complexes of Co(II). For [Co(H 2 O) 6] 2+, which is pink, ε ≈ 10. For [CoCl 4] 2-, which is deep blue, ε ≈ 600. [5]
The Renner-Teller effect is a phenomenon in molecular spectroscopy where a pair of electronic states that become degenerate at linearity are coupled by rovibrational motion. [ 1 ] The Renner-Teller effect is observed in the spectra of molecules that have electronic states that allow vibration through a linear configuration.
Complexes such as this are called "low spin". For example, NO 2 − is a strong-field ligand and produces a large Δ. The octahedral ion [Fe(NO 2) 6] 3−, which has 5 d-electrons, would have the octahedral splitting diagram shown at right with all five electrons in the t 2g level. This low spin state therefore does not follow Hund's rule.