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

A new polymorph of volborthite [tricopper(II) divanadium(V) hepta­oxide dihydroxide dihydrate], Cu3V2O7(OH)2·2H2O, 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 Cu3O6(OH)2 layers composed of edge-sharing CuO4(OH)2 octa­hedra, with V2O7 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 CuII spins in the kagome lattices embedded in the Cu3O6(OH)2 layers.