Synthesis and Structure of a New Copper(II) Pyroarsenate, BaCuAs2O7

Abstract

Single crystals of a new barium copper(II) pyroarsenate, BaCuAs2O7, were grown via an eutectic flux of 40% BaCl2 and 60% NaCl by moles. The structure of this pyroarsenate has been determined by single-crystal X-ray diffraction methods. The title compound crystallizes in the monoclinic system with the space group P 21/n (No. 14); Z = 4. The lattice parameters are a = 5.740 (5) Å, b = 8.475 (3) Å, c = 13.090 (3) Å, β = 91.24 (4)°, and V = 636.7 (6) Å3. The final least-squares full-matrix refinements yielded R/Rw = 0.030/0.043 and GOF = 1.81 for 101 variables. The newly synthesized BaCuAs2O7 phase is isostructural with ACuP2O7 (A = Ca, Sr). The unit cell adopts an open framework structure that consists of corner-shared CuO5 square pyramid and As2O7 pyroarsenate groups; Ba atoms occupy the gap between two layered-like [CuAs2O7] frameworks. It is recognized, for the first time, that the gap between parallel [CuAs2O7] slabs is characterized by a long Cu-O apical bond, 2.386 (3) Å; this length is dictated by the size of the barium cation. In this paper, the flux synthesis, structural analysis, and infrared study of BaCuAs2O7 are presented.