PbMSeO6 (M = Mo and W): New quaternary mixed metal selenites with asymmetric cationic coordination environments

Abstract

Two new isostructural mixed metal selenites, PbMSeO₆ (M = Mo⁶⁺ or W⁶⁺), that are only composed of second-order Jahn-Teller (SOJT) distortive cations have been synthesized by standard solid-state reaction techniques using PbO, SeO₂, and MoO₃ (or WO₃) as reagents. The structures of the reported materials were determined by single-crystal and powder X-ray diffraction. The materials show a three-dimensional framework structure consisting of chains of corner-shared MO₆ octahedra connected by SeO₃ and PbO₈ polyhedra. All of the constituent cations (M⁶⁺, Se⁴⁺, and Pb²⁺) are in distorted environments attributable to second-order Jahn-Teller (SOJT) effects. While the Mo⁶⁺ cations undergo a C₂-type intraoctahedral distortion toward an edge, the Se⁴⁺ and Pb²⁺ cations are in asymmetric coordination environments attributable to their lone pairs. The SeO₃ polyhedra strongly influence the direction of the Mo⁶⁺ intraoctahedral distortion. Infrared spectroscopy, thermogravimetric analysis, the magnitudes of out-of-center distortions, and dipole moment calculations are also presented. Crystal data: PbMoSeO₆, triclinic, space group P-1 (No. 2), with a = 6.8944(6) Å, b = 7.2219(6) Å, c = 10.8294(9) Å, α = 99.751(2)°, β = 99.996(2)°, γ = 90.041(2)°, V = 523.09(8) ų, and Z = 2; PbWSeO₆, triclinic, space group P-1 (No. 2), with a = 6.8689(2) Å, b = 7.2398(2) Å, c = 10.9037(3) Å, α = 99.699(4)°, β = 100.348(3)°, γ = 90.139(4)°, V = 525.50(3) ų, and Z = 2.