REDUCED MOLYBDENUM-NIOBIUM OXIDES .2. CRYSTAL-STRUCTURE OF (MO, NB)(13)O-33

(Mo, Nb)13O33 crystallizes in the triclinic system, space group P1 (No. 2). The unit cell dimensions are a = 3.8194(4) Å, b = 11.2898(7) Å, c = 14.9764(9) Å, α = 94.039(5)°, β = 97.326(6)°, γ = 99.748(7)°, V = 628.47(9) Å3, and Z = 1. The structure was refined to R = 0.032, Rw = 0.036, with 1460 observed reflections (I < 3σ(I)) and 186 variable parameters. The structure of (Mo, Nb)13O33 is related to the crystallographic shear structure of the Nb2O5-δ family and is built up from the 3 × 4 × ∞ building blocks of the ReO3-type MO6 octahedra (M = Mo, Nb) and strings of edge-sharing MoO4 tetrahedra running along [101]. The 3 × 4 ReO3-type slabs at different heights along [101] are interconnected through corner sharing with the MoO4 tetrahedra. (Mo, Nb)13O33 is an insulator at room temperature. © 1994 Academic Press, Inc.