Crystal structures of the high temperature forms of V₈O ₁₅ and V₉O₁₇ and structural trends in the V_nO_2n-1 Magnéli 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) Å, b=7.0142(9) Å, c=14.5252(19) Å, α=97.0310(10)°, β=90.9900(10)°, γ=108.9630(10)°, V=517.53(12) ų, and Z=2. We also report refinement of the structure of metallic ht-V₈O₁₅, space group=P-1, a=5.4315(17) Å, b=7.015(2) Å, c=13.147(5) Å, α=100.144(4)°, β=95.776(4)°, γ=108.965(3)°, V=459.6(3) ų, and Z=2. The structure of metallic V ₉O₁₇ is interpreted and discussed in the context of the V_nO_2n-1 Magnéli 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.