A NEW LAYERED VANADIUM SELENIUM OXIDE WITH A STRUCTURE RELATED TO HEXAGONAL TUNGSTEN-OXIDE - NH4(VO2)(3)(SEO3)(2)

The compound NH4(VO2)(3)(SeO3)(2) has been prepared by hydrothermal sy nthesis at 200 degrees C from V2O5, SeO2, and NH4Cl. The crystal struc ture was determined by single-crystal X-ray diffraction. Crystal data: NH4(VO2)(3)(SeO3)(2), M(r) = 410.79; hexagonal, space group P6(3) (No . 173); cell parameters a = 7.137(3) Angstrom A, c = 11.462(4) degrees A, V = 505.7(4) Angstrom A(3), Z = 2; R(F) = 0.0416 and R(w)(F-2) = 0 .1041 (515 reflections). The structure consists of hexagonal layers of corner-sharing VO6 octahedra. The apical oxygen atoms of the VO6 octa hedral are capped by Se atoms that form SeO32- groups; the ammonium io ns are located between adjacent layers. The structure contains the fir st example of a hexagonal tungsten bronze type layer where the octahed ral cation is vanadium. Redox intercalation reactions similar to those reported for VOPO4 H2O were studied but are complicated by the ease o f reduction of the SeO32- group to selenium metal accompanied by decom position of the vanadium-oxygen layers acid the formation of V2O5.