Synthesis and crystal structure of Cs2Nb6Br5F12:: A Nb6 cluster compound with a one-dimensional Nb6Br5iF7iF6a unit connection

The synthesis and the crystal structure of Cs2Nb6Br5F12 containing octahedral niobium clusters are presented in this work. This bromoflouride is based on a (Nb6L12F6a)-F-i (L= Br and F) unit and crystallizes in the orthorhombic system (space group, Cecin; Z = 4; a = 9.2446(2) Angstrom, b = 13.6256(3) Angstrom, and c = 17.1665(4) Angstrom; R = 0.0241). Fluorine and bromine are randomly distributed on the inner ligand positions, L', that edge-bridge the Nb, cluster whereas fluorine fully occupies the apical positions (L'). The units are linked to each other by apical ligands leading to an original one-dimensional unit connection. The cesium atoms are statistically distributed on several sites that describe parallel channels along the [10 0] direction. The influence of fluorine ligands upon the stabilization of this structure type as well as the structural relationships with Ba2Zr6Cl17(B), Nb6F15, and NaMo6Cl13 will be evidenced and discussed. (C) 2002 Elsevier Science.