CRYSTAL-STRUCTURE OF NH4[GA2(PO4)2(OH)(H2O)], H2O, ISOTYPIC WITH ALPO4-15

NH4[Ga2(PO4)2(OH)(H2O)],H2O was obtained in a pure form by hydrotherma l synthesis (453 K, 24 h, autogeneous pressure) from a mixture of Ga2O 3, P2O5, HF, guanidine and H2O in the ratio 1:2:2:1.3:80. It is monocl inic (space group P2(1)/n (n-degree-14)) with a = 9.689(1) angstrom, b = 9.703(1) angstrom, c = 9.788(1) angstrom, beta = 102.78(2)-degrees, V = 897.4(4) angstrom3, Z = 4. The structure, refined to R(W) = 0.026 , R = 0.025, is similar to the previously described Ga(PO4), 2 H2O, le ucophosphite, AlPO4-15 and GaPO4-C7. The framework is built up from co rner linked octameric [Ga4(PO4)4(OH)2(H2O)2] units, in which gallium i s exclusively in octahedral coordination. NH4+ ions and one half of th e water molecules are inserted in the cavities between the octamers.