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

Abstract

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 RbO_<i>n</i> (<i>n</i> = 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 <i>Fddd</i> (No. 70), <i>a</i> = 11.012(5) Å, <i>b</i> = 12.403(5) Å, <i>c</i> = 15.839(7) Å, <i>V</i> = 2163.3(16) ų, and <i>Z</i> = 16; Rb₄­Mo₅P₂­O₂₂, orthorhombic, space group <i>C</i>222₁ (No. 20), <i>a</i> = 6.5300(5) Å, <i>b</i> = 19.7834(18) Å, <i>c</i> = 17.3451(15) Å, <i>V</i> = 2240.7(3) ų, and <i>Z</i> = 4