STRUCTURE OF RBALAS2O7

Rubidium aluminium pyroarsenate, M(r) = 374.29, triclinic, P1BAR, a = 8.233 (5), b = 6.34 (2), c = 6.241 (5) angstrom, alpha = 102.6 (1), beta = 103.89 (7), gamma = 96.7 (1)-degrees, V = 303.9 angstrom3, Z = 2, D(m) = 3.9 (3) (pycnometry), D(x) = 4.09 g cm-3, lambda(Ag KalphaBAR) = 0.5608 angstrom, mu = 108.14 cm-1, F(000) = 344, T = 296 K, R = 0.049, wR = 0.053 for 2193 reflections. The first structural investigation on a pyroarsenate is reported. It is built from AlAs2O11 units comprising one AlO6 octahedron and one As2O7 pyroarsenate group in which two AsO4 tetrahedra point in opposite directions. These units are connected by heteropolyhedral linkages to form a three-dimensional framework having intersecting tunnels where the Rb+ ions are located. Although this structure is not isotypic with the phosphate analogues, it is closely related to that of the pyrophosphates of type I represented by KAlP2O7.