RB4AL2NB35O70 - A NEW REDUCED NIOBATE WITH ISOLATED NB6 OCTAHEDRAL CLUSTERS

Single crystals of the new reduced niobium oxide, Rb4Al2 Nb35O70, were grown by heating mixtures of Na3NbO4, NbO, and RbCl in an alumina boa t, sealed in a fused silica tube. Rb4Al2 Nb35O70 crystallizes in the t rigonal space group P3BAR: a = 7.815(1) angstrom, c = 26.392(9) angstr om, with one formula unit per unit cell. The structure was determined from single crystal X-ray diffraction data and refined to an R value o f 3.39%. Three distinct types of niobium atom coordination environment s exist in this structure including isolated NbO6 octahedra, Nb3O13 tr iangular clusters formed by 3 face-shared NbO6 octahedra, and Nb6 octa hedral clusters of the type [Nb6O12]O6. (C) 1994 Academic Press, Inc.