A SINGLE-CRYSTAL AND SYNCHROTRON POWDER X-RAY REFINEMENT OF THE STRUCTURE OF SRNB8O14, A NEW OXONIOBATE CONTAINING NB-6 OCTAHEDRA

Single crystals of SrNb8O14 were prepared by heating a pellet of SrNb2-O6, NbO, Nb (1:1:1) and B2O3 (as mineralizer) at 950°C for seven days. Using single-crystal data, the crystal structure could be solved and refined (R=3.9%, Rw=3.0%). The compound crystallizes in Pbam with a=925.7(4)pm, b=1030.1(6) pm, c=595.4(3) pm and Z=2. A synchrotron X-ray powder study leads to a=925.2(1) pm, b=1029.6(1) pm, c=595.6(1) pm and parameters which are in good agreement with those obtained from single-crystal data. Characteristic building groups of the new structure type are Nb6O12 clusters, NbO6 octahedra (Nb5+) and SrO12 cube octahedra. The clusters are connected via oxygen atoms forming a three-dimensional network. The Madelung part of the lattice energy (MAPLE) was calculated and is discussed.