Synthesis and Characterization of Se₄Nb₂O₁₃:  A New Ternary Se⁴⁺−Nb⁵⁺−Oxide with Monoselenite and Diselenite Groups

A new noncentrosymmetric ternary selenite, Se₄Nb₂O₁₃, has been synthesized from SeO₂ and Nb₂O₅. Crystal data:  Se₄Nb₂O₁₃, M_r = 709.64, monoclinic, space group Pa (No. 7), a = 7.555(6) Å, b = 6.637(8) Å, c = 11.377(5) Å, β = 109.23(3)°, V = 538.64(2) ų (T = 200 K), Z = 2, R(F) = 6.44%, R_w(F) = 7.12%. The compound consists of rows of corner-linked NbO₆ octahedra that are also connected through monoselenite, SeO₃, and diselenite, Se₂O₅, groups.