Experimental versus expected halide-ion size differences; structural changes in three series of isotypic bismuth chalcogenide halides

Abstract

Experimentally determined halide-ion size differences are compared with expected size differences in the three series of isotypic bismuth chalcogenide halide compounds, KBi6O9 X (X = Cl, Br and I), BiOX (X = F, Cl, Br and I) and BiSX (X = Cl, Br and I). The strong deviations observed can be assigned to steric strain caused by the heterogenity of the bond-valence pattern and (for BiOX) to anion–anion repulsion and a change in the connectivity scheme. Some special features of the BiOF structure and the question of `isotypism' within the BiOX series are briefly discussed. Structural changes within the BiSX series are analysed.