Crystal structures of the high temperature forms of V8O15 and V9O17 and structural trends in the VnO2n-1 Magneli series

We report the structure of the metallic high-temperature (ht) form of V9O17, determined from single crystal X-ray diffraction: space group = P-1 a = 5.4219(7) angstrom, b = 7.0142(9) angstrom, c = 14.5252(19) angstrom, alpha = 97.0310(10)degrees, beta = 90.9900(10)degrees, gamma = 108.9630(10)degrees, V = 517.53(12) angstrom(3), and Z = 2. We also report refinement of the structure of metallic ht-V8O15, space group = P-1, a = 5.4315(17) angstrom, b = 7.015(2) angstrom, c = 13.147(5) angstrom, alpha = 100.144(4)degrees, beta = 95.776(4)degrees, gamma = 108.965(3)degrees, V = 459.6(3) angstrom(3), and Z = 2. The structure of metallic V9O17 is interpreted and discussed in the context of the VnO2n - 1 Magneli phases, yielding trends about how the underlying forces contribute to the metal to insulator transition (MIT). The manner in which structural features of the metallic phases change as a function of n supports previous arguments that there is a turnover in the forces leading to the MIT between n = 6 and n = 8. (c) 2012 Elsevier Inc. All rights reserved.