6s2 Lone Pair Effects in related structures PbO, BiOF and Bi2NbO5F: Crystal chemistry and DFT investigations

Based on the stereochemistry of 6s 2 (E) lone pair elements Pb II and Bi III , designated by M*, the related PbO, BiOF and Bi2NbO5F crystal structures were revisited. Lone pair presence determined by its sphere of influence E, equal to those of oxygen or fluorine anions, was settled by its center then giving M*-E directions and distances. Detailed description of structural features of both elements in these three compounds characterized by [PbEO]n and [BiEO]n layers allowed to show the evolution of M*-E versus the coordination polyhedra. All are different, in red PbO one finds {PbEO4E4} square antiprism, a {[Bi.E]O4F4Fapical} monocapped square antiprism in BiOF and {BiEO4F4}square antiprism in Bi2NbO5F. To analyze the crystal chemistry results, the electronic structures of these compounds were calculated within density functional theory DFT. Real space analyses of electron localization illustrate a full volume development of the lone pair on Pb II within {PbEO4E4} and Bi III within {BiEO4F4} square antiprisms, contrary to Bi III within {[Bi.E]O4F4Fapical} monocapped square antiprism. Larger hardness and band gap characterize BiOF versus PbO due to the presence of F which brings antibonding Bi-F interactions oppositely to mainly bonding Bi-O.  2014 Elsevier Ltd. All rights reserved.