A novel crystal polymorph of volborthite, Cu3V2O7(OH)2·2H2O.

A new polymorph of volborthite [tricopper(II) divanadium(V) heptaoxide dihydroxide dihydrate], Cu(3)V(2)O(7)(OH)(2)·2H(2)O, has been discovered in a single crystal prepared by hydrothermal synthesis. X-ray analysis reveals that the monoclinic structure has the space group C2/c at room temperature, which is different from that of the previously reported C2/m structure. Both structures have Cu(3)O(6)(OH)(2) layers composed of edge-sharing CuO(4)(OH)(2) octahedra, with V(2)O(7) pillars and water molecules between the layers. The Cu atoms occupy two and three independent crystallographic sites in the C2/m and C2/c structures, respectively, likely giving rise to different magnetic interactions between Cu(II) spins in the kagome lattices embedded in the Cu(3)O(6)(OH)(2) layers.