Bond valence as an aid to understanding the stereochemistry of O and F complexes of Sn(II), Sb(III), Te(IV), I(V) and Xe(VI)

The calculation of bond valences (S) from the bond lengths (R) observed in 63 different crystals using the relation s = so(R/Ro−N allows a direct quantitative comparison of the bonding in a variety of different complexes formed between A and X atoms where A = Sn(II), Sb(III), Te(IV), I(V) and Xe(VI) and X = 0 and F. The environment of A is usually an octahedron which has been distorted so that the weak bonds occur opposite strong bonds and bonds of intermediate strength occur opposite each other. The possible environments form a continuous series from one having 2 strong, 2 intermediate, and 2 weak bonds ((A)) through one having 3 strong and 3 weak bonds ((C)) to one having 1 strong, 1 weak and 4 intermediate bonds (ɛ). The particular environment observed is related to the ratio of the valences of A and X, a ratio of 2 leading to a configuration close to A, 3 close to C and 5 close to ɛ. Specific bond valences can be associated with strong, intermediate and weak bonds for each pairs of atoms A-X and the angles between any 2 strong bonds is equal to (73 + 17 〈 s 〉) degrees where 〈 s 〉 is their average bond valence. These principles lead to a natural explanation of the O and F bridges frequently found in these complexes and the influences such bridges have on the detailed environment of A.