Influence of lone-pair electrons of cations on bond-valence parameters

According to the current bond-valence concept, the valence Vi of an atom A i is a function of the distances Dij to its neighbors X j and can be calculated using Vi = [unk] Sij = [unk] exp [(r 0 − Dij )/0.37], where the bond-valence parameter r 0 is considered to be constant for each element pair A–X. A statistical analysis based on 1924 [LXm] polyhedra is presented, where L are cations having one electron lone-pair and X = O, S or Se. According to this analysis, for i r 0 for each individual [LXm] polyhedron is dependent on the stereochemical influence of the lone-pair electrons on the geometry of the polyhedron. This influence is expressed by a vector [unk] i = [unk]([unk]X j − L i − X j′, Dij ). As a result, the formal bond-valence sum for an individual lone-pair cation L i can be calculated with [unk]Sij = [unk]exp [(E|[unk] i | + F − Dij )/0.37] where E and F are constants.