HYDROTHERMAL SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF 4 LAYERED VANADYL(IV) PHOSPHATE HYDRATES A(VO)2(PO4)2.4H2O (A = CO, CA, SR, PB)

The single crystals of four vanadyl (IV) phosphate hydrates A(VO)2(PO4)2.4H2O (A = Co, Ca, Sr, Pb) were grown hydrothermally at 230-degrees-C and were characterized by single-crystal X-ray diffraction and thermal analysis. Crystal data: Co(VO)2(PO4)2.4H2O, tetragonal, I4/mmm, a = 6.264 (1) angstrom, c = 13.428 (4) angstrom, V = 526.9 (2) angstrom3, Z = 2, and R = 0.0527; Ca(VO)2(PO4)2.4H2O, triclinic, P1, a = 6.3484 (8) angstrom, b = 6.350 (1) angstrom, c = 6.597 (1) angstrom, alpha = 106.81 (2)-degrees, beta = 94.09 (1)-degrees, gamma = 90.02 (1)-degrees, V = 253.86 (8) angstrom3, Z = 1, and R = 0.0221; Sr(VO)2(PO4)2.4H2O, monoclinic, Cc, a = 9.026 (2) angstrom, b = 9.010 (3) angstrom, c = 12.841 (3) angstrom, beta = 100. 19 (2)-degrees, V = 1027.8 (1) angstrom3, Z = 4, and R = 0.0350; Pb(VO)2(PO4)2.4H2O, monoclinic, Cc, a = 9.030 (3) angstrom, b = 9.021 (2) angstrom, c = 12.874 (4) angstrom, beta = 100.16 (2)-degrees, V = 1032.3 (5) angstrom3, Z = 4, and R = 0.0307. All four structures contain layers of vanadium phosphorus oxide with the water molecules and divalent metal cations between the layers. The layer is a 4-connected net in which corner-sharing vanadium oxygen polyhedra and phosphate tetrahedra alternate. In Co(VO)2(PO4)2.4H2O the vanadium is 5-coordinated in form of square pyramids. In the Ca, Sr, and Pb compounds, the vanadium oxygen polyhedra are distorted octahedra. The Co compound contains units of linear V=O-Co-O=V. The structure of the Ca compound reported in this work is a triclinic polymorph of the rare mineral sincosite. The Sr and Pb compounds are isostructural. The four structures are discussed along with the parent VOPO4.2H2O.