Crystal structure and magnetic properties of Na9V14O35:: Sodium-vanadium bronze η-NaxV2O5

The crystal structure of eta-Na1.3V2O5, a member of NaxV2O5 bronze family, has been determined by single-crystal X-ray study: its actual stoichiometric formula is denoted by Na9V14O35. The monoclinic system P2/c was confirmed with a = 15.209(8) Angstrom, b = 5.036(5) Angstrom, c = 20.786(6) Angstrom, beta = 109.18(3)degrees with Z = 2, The refinements converged to R = 0.036 and R-w = 0.037 for 3848 reflections with I > 3 sigma(I), The structure is of a layer type consisting of V2O5 layers and interlayer Na atoms. The V2O5 layer adopts a novel framework built up with edge-sharing VO5 square pyramids for five V atoms (four V4+ and one V4.5+) and vertex-sharing VO4 tetrahedra for two V atoms (V5+). Low-dimensional behavior with a spin gap was observed in the magnetic susceptibility but the structure is dissimilar to any structure type of low-dimensional spin-gap systems, The compound probably presents a new type of spin-gap system. (C) 1999 Academic Press.