Synthesis and structural study of copper(II) diarsenates

Three new copper(II) diarsenates, ACuAs(2)O(7) (A = Ca, Sr, Ba), have been synthesized hydrothermally and characterized by single-crystal X-ray diffraction. All three compounds crystallize in monoclinic system with Z = 4. Crystal data: CaCuAs2O7, a = 7.248(2) Angstrom, b = 8.952(2) Angstrom, c = 9.258(2) Angstrom, beta = 109.66(2)degrees, V = 565.7(3) Angstrom(3), space group P2(1)/c, R = 0.0327; SrCuAs2O7, a = 5.550(1) Angstrom, b = 8.299(2) Angstrom, c = 12.858(3) Angstrom, beta = 91.75(3)degrees, V = 592.0(3) Angstrom(3), space group P2(1)/n, R = 0.0207; BaCuAs2O7, a = 5.736(1), b = 8.458(2), c = 13.044(3) Angstrom, beta = 91.16(3)degrees, V = 632.7(3) Angstrom(3), space group P2(1)/n, R = 0.0373. The structures of these compounds consist of corner-sharing CuO5 square pyramids and As2O7 disarsenate units. The calcium compound adopts a new structural type. The strontium compound is isotypic with the phosphate analog SrCuP2O7 (Moqine et al., J. Solid State Chem. 107, 368, 1993). The barium compound adopts the same structure as SrCuAs2O7 instead of the triclinic BaCuP2O7 (Moqine et al. Acta Crystallogr. C47, 2294, 1991). The relationship between (R(A)-R(B)) and space group symmetry as observed in the A(II)B(II)P(2)O(7) system (Elmarzouki et al., ACA abstract L07, 1994) does not exist in this diarsenate system. The structures of these diarsenates are discussed along with their phosphate analogues. (C) 1996 Academic Press, Inc.