Correlation of angular and bond length distortions in TO4 units in crystals

Abstract The bond lengths, edge lengths and angular distortions were evaluated for 311 TO4 units of distorted tetrahedral symmetry for 16 T elements in 191 compounds and for three ZnCl4 units. The bond length distortions increase fairly regularly with decreasing size of the central ion while the edge lengths and angular distortions have minima close to the ionic radius of P5+. The transition metal ions V5+, Cr6+, Mo6+ and Zn2+ and to some extent also second row elements follow the general trends observed for the other central ions. The average ratio of bond lengths to angular distortions also increases with decreasing ionic radius to a maximum at P5+. Possible influences of the valence of the central ion are also discussed. The distortions of the ZnCl4 units are considerably smaller than the average of the ZnO4 units, most likely as a result of the larger ionic size of the anions. There also appears to be an effect of the counterions since for ClO4 − units in compounds of very bulky cations the average bond lengths are smaller and the average distortions are several times larger than in alkali and ammonium Perchlorates. The distortions also seem to increase with temperature.