Coordination in inorganics

Tetrahedral distortion values are calculated as the mean quadratic elongation and the bond angle variance for 63 MX4 tetrahedra (M=transition metal or thallium, X=Cl→I). The degree of distortion according to these two geometrical parameters are more or less linearily correlated. The magnitude of the distortion is affected by the ratio of the central to vertex atom radii, and by the character of the atoms surrounding the vertex atoms. The tendency is that the heavier the elements, the lower the degree of distortion. Simulated distortion modes could not be assigned to the observed ones. However, the presented results from the observed MX4 tetrahedra suggest that the distortions are attributed to effects related to the crystal structure and chemistry rather than to any strictly mathematical phenomena.