Synthesis, crystal structure, and physical properties of Sr_0.93 (Si(x)Nb(1-x)) Nb₁₀O₁₉ (x = 0.87)

We present here the synthesis, crystal structure, and physical properties of a reduced niobium oxide Sr_0.93(Si(x)Nb(1-x))Nb₁₀O₁₉ (x = 0.87). Its structure was determined on single crystal by X-ray diffraction in the space group R3̄ (a(h) = 7.843(1), C(h) = 42.26(2) Å, V(h) = 2251.3(9) ų, and Z = 6). The compound is isostructural to Na(Si(x)Nb(1-x)) Nb₁₀O₁₉ (x ≃ 0.75) and exhibits discrete [Nb₆O₁₂] clusters, Nb₂O₁₀ dimers, NbO₆ octahedra, SrO₁₂ cubo-octahedra, and SiO₄ tetrahedra. The compound is insulating with a room-temperature resistivity ˜50 Ω cm. The magnetic susceptibility data yields μ(eff) = 3.16 μ(B)/Nb, which is consistent with a 15-electron [Nb₆O₁₂] cluster, with Nb(IV) in the dimers and Nb(V) in the isolated NbO₆ octahedra. (C) 2000 Academic Press.