Stabilization energies in distorted coordination sites

As noted in 2.11, ligands forming high-symmetry coordination polyhedra (i.e., regular octahedra, tetrahedra, cubes and dodecahedra) about central transition metal ions are rare. Such highly idealized coordinations, nevertheless, do exist in the periclase (octahedra), cubic perovskite (octahedra, dodecahedra) and spinel (tetrahedra) structures. The more important rock-forming oxide and silicate minerals provide, instead, low-symmetry coordination environments. These include trigonally distorted octahedra in the corundum, spinel and gar- 

Distorted coordination sites in oxides and silicates have several important consequences in transition metal geochemistry and crystal chemistry. First, 

Electronic structure Cation Electronic configuration Octahedron elongated along tetrad axis Octahedron compressed along tetrad axis Configuration of the most stable six-coordinated site 

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The John—Teller effect and stabilization energies in distorted coordination sites. Transition metal ions rarely occur in high-symmetry coordination sites in silicate minerals, which show various distortions from regular octahedral,... 

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