CRYSTAL-STRUCTURES OF AG5CU(ASO4)(AS2O7) AND AG7CU(AS2O7)2CL WITH A SURVEY ON PYROARSENATE ANIONS

The crystal structures of two hydrothermally synthesized Ag-Cu-arsenat es were determined by single crystal X-ray work: Ag5Cu(ASO4)(AsO7) [a = 5.859(1), b = 9.019(2), c = 10.384(2) angstrom, alpha = 97.18(2), be ta = 90.98(2), gamma = 92.11(2)-degrees, space group P1BAR, Z = 2, R(w ) = 0.034 for 5827 observed data and 185 variable parameters] and Ag7C u(AS2O7)2Cl [a = 10.335(2), b = 8.992(2), c = 16.546(3) angstrom, beta = 95.21(2)-degrees, space group Cc, Z = 4, R(w) = 0.035 for 3202 obse rved reflections and 243 variable parameters]. The environment of the Cu atom in Ag7Cu(AS2O7)2Cl is peculiar: the Cu-O bond lengths of 1.914 (7), 1.945(6), 2.136(8), 2.147(7), 2.250(8), and 2.344(7) angstrom sho w an uncommon [2 + 2 + 2] coordination (distorted octahedron). The two Cu atoms in Ag5Cu(ASO4)(AS2O7) are [4] and [4 + 2] coordinated, all t he Ag atoms are irregularly [5], [6], and [7] coordinated to O (and Cl ) atoms. The geometry of the pyroarsenate groups are compared to data from literature.