Synthesis and Crystal Structure of Rb1.5(NH4)0.5{Cu(P2O7)}: Comparative Crystal Chemistry and Topology‒Symmetry Analysis in Terms of Extended OD Theory

Abstract

A new compound of the Rb_1.5(NH₄)_0.5{Cu(P₂O₇)} composition, obtained by the high-temperature reaction method from a mixture of RbNO₃, Cu(NO₃)₂, and (NH₄)₄P₂O₇, has been studied using X-ray diffraction. This compound is crystallized in the orthorhombic system, sp. gr. Pnma, a = 15.146(3) Å, b = 5.183(1) Å, c = 10.096(2) Å, V = 792.6(3) ų. The structure has been interpreted and refined to the final reliability factor R₁ = 6.56% in the anisotropic approximation of atomic displacements, using 415I > 3σ(I). Rb_1.5(NH₄)_0.5{Cu(P₂O₇)} belongs to the group of copper diorthophosphates of alkaline elements, described by the general formula \(A_{2}^{ + }\){Cu(P₂O₇)}. The basis of its crystal structure is a set of polar heteropolyhedral copper-phosphate layers of the {Cu(P₂O₇)}^2–_∞∞ composition, formed by vertex-sharing CuO₅ pyramids and tetrahedral diorthogroups P₂O₇, which are linked via rubidium cations. Based on symmetry interlayer connections, one can predict a series of partially ordered structures using the following groupoid: λ-PO P(n)m2₁; σ-PO P12₁/m1 || Pсm2₁.