The single crystals of four vanadyl(1V) phosphate hydrates A(VO)2(P04)2.4H20 (A = Co, Ca, Sr, Pb) were grown hydrothermally at 230 OC and were characterized by single-crystal X-ray diffraction and thermal analysis. Crystal data: Co(V0)2(P04)2.4H20, tetragonal, Mlmmm, a = 6.264 (1) A, c = 13.428 (4) A, V = 526.9 (2) A3, Z = 2, and R = 0.0527; Ca(V0)2(P04)2.4H20, triclinic, P1, a = 6.3484 (8) A, b = 6.350 (1) A, c = 6.597 (1) A, a = 106.81 (2)O, ,8 = 94.09 (1)O, y = 90.02 (1)O, V = 253.86 (8) A3, Z = 1, and R = 0.0221; Sr(VO)2(P04)2.4Hz0, monoclinic, Cc, a = 9.026 (2) A, b = 9.010 (3) A, c = 12.841 (3) A, ,8 = 100.19 (2)O, V = 1027.8 (1) A3, Z = 4, and R = 0.0350; Pb(VO)2(P04)2.4H20, monoclinic, Cc, a = 9.030 (3) A, b = 9.021 (2) A, c = 12.874 (4) A, ,8 = 100.16 (2)O, V = 1032.3 (5) A3, Z = 4, and R = 0.0307. All four structures contain layers of vanadiumphosphorus 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(V0)2(P04)24H20 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 VOP04.2H20.

A new dioxovanadium(v) phosphate, Ag,VO,PO,, has been synthesised hydrothermally at 230 "C and characterized by single-crystal X-ray diffraction. The compound crystallizes in the monoclinic space group C2/m with a = 12.431( 3), b = 6.298(1). c = 6.300(2) A, p = 90.38(2)", Z = 4 and R = 0.026. The structure consists of layers of dimers of edge-sharing VO, octahedra and PO, tetrahedra, extending parallel to the (001 ) crystallographic plane with silver ions between the layers. The structural relationship with BaVO,PO, is discussed. Alternating current impedance measurements on Ag,VO,PO, indicate that the ionic conductivity at 375 "C is 1 x 1 O-, 0-' cm-l with an activation energy of 47 kJ mol-'.Although a large number of new compounds have been synthesised and structurally characterized in the A-V-P-0 (A = metal cation) system containing vanadium in oxidation states less than +5,'-, considerably less structural work has been reported on the A-V5 + -P a system. To our knowledge, AV02HP04 (A = NH,+, K + , Rb+ or TI+),*' and AV02P0, (A = Ba2 + or Sr2+) are essentially the only structurally well characterized examples. The former structure consists of isolated chains of VO, square pyramids. Adjacent VO, units in each chain are bridged by HPO, groups. The latter structure comprises layers of phosphate tetrahedra and edge-sharing bioctahedra, which contain two distorted VO, octahedra, with divalent metal cations between the layers.Attempts to add new members to the A-VS+-P-O system have yielded the layered dioxovanadium(v) phosphate Ag,VO,PO, the structure of which is related to that of AVO,PO, (A = Ba2+ or Sr2+). This work reports the hydrothermal synthesis, single-crystal structure, and ionic conductivity of Ag2V02P04, and forms a part of our programme to search for new solid electrolytes.

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