Crystal structure of Cs2GdNb6Cl15O3 in the structural evolution of niobium oxychlorides with octa-hedral Nb6-cluster units

Abstract

Cs₂GdNb₆Cl₁₅O₃, dicaesium gadolinium hexa-niobium penta-deca-chloride trioxide, was synthesized by solid-state reactions starting from a stoichiometric mixture of CsCl, Gd₂O₃, Nb, NbCl₅, and Nb₂O₅. The crystal structure is based on octa-hedral Nb₆ cluster units (point group symmetry 3.2) with composition [(Nb₆Clⁱ ₉Oⁱ ₃)Cl^a ₆]^5- where i and a denote inner and outer ligands. Cs₂GdNb₆Cl₁₅O₃ exhibits 14 valence electrons per cluster unit. The cluster units are linked to each other by Cs^I and Gd^III atoms, whereby Cs^I (site symmetry 3..) is 12-coordinated by six Clⁱ and six Cl^a ligands belonging to six neighboring cluster units and Gd^III (site symmetry 3.2) is 9-coordinated by three Oⁱ and six Clⁱ ligands belonging to three adjacent cluster units. The arrangement of cluster units corresponds to a stacking of …AA'A… layers along [001]. Cs₂GdNb₆Cl₁₅O₃ is isotypic with Cs₂UNb₆Cl₁₅O₃.

Keywords: cluster compound; crystal structure; valence electron count.