Soft chemistry synthesis and crystal structure of MgxCu3−xV2O6(OH)4·2H2O

MgxCu3−xV2O6(OH)4·2H2O (x ∼ 1), with similar crystal structure as volborthite Cu3V2O7(OH)2·2H2O, was successfully prepared by a soft chemistry technique. The method consists of mixing magnesium nitrate and copper nitrate with a boiling solution of vanadium oxide (obtained by reacting V2O5 with few mL of 30 vol.% H2O2 followed by addition of distilled water). When ammonium hydroxide NH4OH 10% was added (pH 7.8), a green yellowish precipitate was obtained. Using X-ray powder diffraction data, its crystal structure has been determined by Rietveld refinement. Compared to volborthite, the vanadium coordination changes from tetrahedral VO4 to trigonal bipyramidal VO5, and magnesium replaces copper, preferably, in the less distorted octahedron. At 300 °C, the phase formed is similar to the high pressure (HP) monoclinic Cu3V2O8 phase. However at higher temperature, 600 °C, the phase obtained is different from known Cu3V2O8 phases.