New Molybdenum(VI) Phosphates: Synthesis, Characterization, and Calculations of Centrosymmetric Rb­MoO₂­PO₄ and Noncentrosymmetric Rb₄­Mo₅P₂­O₂₂

Two new molybdenum­(VI) phosphates, Rb­MoO2­PO4 and Rb4­Mo5P2­O22, have been synthesized by standard solid-state reactions, and their structures were determined by single-crystal X-ray diffraction. The former is centrosymmetric, whereas the latter is noncentrosymmetric and chiral. Their crystal structures both consist of corner- and edge-shared MoO6 octahedra, PO4 tetrahedra, and RbOn (n = 8 or 10) polyhedra and exhibit three- and one-dimensional structures, respectively. Powder second-harmonic generation (SHG) measurements revealed an SHG efficiency of approximately 1.4 × KH2PO4 (KDP) for Rb4­Mo5P2­O22. Thermal analysis, infrared and UV–vis-NIR diffuse reflectance spectroscopy, and electronic band structure calculations were also performed on the reported materials. Crystal data are the following: Rb­MoO2­PO4, orthorhombic, space group Fddd (No. 70), a = 11.012(5) Å, b = 12.403(5) Å, c = 15.839(7) Å, V = 2163.3(16) Å3, and Z = 16; Rb4­Mo5P2­O22, orthorhombic, space group C2221 (No. 20), a = 6.5300(5) Å, b = 19.7834(18) Å, c = 17.3451(15) Å, V = 2240.7(3) Å3, and Z = 4.