A hydrothermal investigation of the 1/2V2O5-H2C2O4/H3PO4/NH4OH system:: Synthesis and structures of (NH4)VOPO4•1.5H2O, (NH4)0.5VOPO4•1.5H2O, (NH4)2[VO(H2O)3]2[VO(H2O)][VO(PO4)2]2•3H2O, and (NH4)2[VO(HPO4)]2(C2O4)•5H2O

The 1/2V(2)O(5)-H2C2O4/H3PO4/NH4OH system was investigated using hydrothermal techniques. Four new phases, (NH4)VOPO4. 1.5H(2)O (1), (NH4)(0.5)VOPO4. 1.5H(2)O (2), (NH4)(2)[VO(H2O)(3)](2)[VO(H2O)][VO(PO4)(2)](2). 3H(2)O (3), and (NH4)(2)[VO(HPO4)](2)(C2O4). H2O (4), have been prepared and structurally characterized. Compounds 1 and 2 have layered structures closely related to VOPO4. 2H(2)O and A(0.5)VOPO(4). yH(2)O (A = mono- or divalent metals), whereas 3 has a 3D open-framework structure. Compound 4 has a layered structure and contains both oxalate and phosphate anions coordinated to vanadium cations. Crystal data: (NH4)VOPO4. 1.5H(2)O, tetragonal (I), space group I4/mmm (No. 139), a = 6.3160(5) Angstrom, c = 13.540(2) Angstrom, Z = 4; (NH4)(0.5)VOPO4. 1.5H(2)O, monoclinic, space group P2(1)/m (No. 11), a = 6.9669(6) Angstrom, b = 17.663(2) Angstrom, c = 8.9304(8) Angstrom, beta = 105.347(1)degrees, Z = 8; (NH4)(2)[VO(H2O)(3)](2)[VO(H2O)][VO(PO4)(2)](2). 3H(2)O, triclinic, space group P (1) over bar (No. 2), a = 10.2523(9) Angstrom, b = 12.263(1) Angstrom, c = 12.362(1) Angstrom, alpha = 69.041(2)degrees, beta = 65.653(2)degrees, gamma = 87.789(2)degrees, Z = 2; (NH4)(2)[VO(HPO4)](2)(C2O4). 5H(2)O, monoclinic (C), space group C2/m (No. 12), a = 17.735(2) Angstrom, b = 6.4180(6) Angstrom, c = 22.839(2) Angstrom, beta = 102.017(2)degrees, Z = 6.