HYDROTHERMAL SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF REDUCED VANADIUM PHOSPHATES, ALPHA-RB[V-III(HPO4)(2)], BETA-RB[V-III(HPO4)(2)] AND NH4[V-III(HPO4)(2)], OCTAHEDRAL-TETRAHEDRAL FRAMEWORK SOLIDS

The vanadium(III) phosphates alpha-Rb[V(HPO4)(2)] (1), beta-Rb[V(HPO4)(2)] (2) and NH4[V(HPO4)(2)] (3) were prepared by hydrothermal reactions of V2O5, vanadium metal, H3PO4, water and an appropriate cation source. The three-dimensional framework of 1 is constructed from the corner-sharing of {VO6} octahedra and {HPO4} tetrahedra which fuse to generate structural motifs based on {V-2(mu(2)-HPO4)(3)} and {V-2(mu(2)-HPO4)(2)} units. The resultant network is characterized by the presence of channels defined by the corner-sharing of four {VO6} octahedra and four {HPO4} tetrahedra and occupied by Rb+ cations. In contrast, the structural motif of 2 is the {V-2(mu(2)-HPO4)(2)} unit exclusively, which produces a framework containing channels defined by the corner-sharing of six {VO6} octahedra and six {HPO4} tetrahedra. Compound 3 is isostructural with 2. Crystal data: Rb15V15P3O12H3 (1), P (1) over bar, a = 8.831(1), b = 9.450(2), c = 7.188(2) Angstrom, alpha = 109.55(2), beta = 110.26(1), gamma = 65.34(1)degrees V = 498.5(2) Angstrom(3), Z = 2, D-calc = 3.261 g cm(-3), structure solution and refinement based on 1047 reflections converged at R = 0.068; RbVP2O8H2 (2), P2(1)/c, a = 5.21(1), b = 8.789(8), c = 14.330(5) Angstrom, beta = 94.39(4)degrees, V = 654(1) Angstrom(3), Z = 4, D-calc = 3.315 g cm(-3), 668 reflections, R = 0.083; VP2O8NH6 (3), P2(1)/c, a = 5.201(2), b = 8.738(2), c = 14.398(3) Angstrom, beta = 94.83(1)degrees, V = 652.0(3) Angstrom(3), D-calc = 2.627 g cm(-3), 1561 reflections, R = 0.052.