Synthesis, Crystal Structure, and Physical Properties of Sr0.93(SixNb1-x)Nb10O19 (x=0.87)

We present here the synthesis, crystal structure, and physical properties of a reduced niobium oxide Sr0.93(SixNb1-x)Nb10O19 (x=0.87). Its structure was determined on single crystal by X-ray diffraction in the space group R (ah=7.843(1), ch=42.26(2) ?, Vh=2251.3(9) ?3, and Z=6). The compound is isostructural to Na(SixNb1-x)Nb10O19 (x0.75) 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 cm. The magnetic susceptibility data yields eff=3.16 B/Nb, which is consistent with a 15electron [Nb6O12] cluster, with Nb(IV) in the dimers and Nb(V) in the isolated NbO6 octahedra.