AVSeO(5) (A=Rh, Cs) and AV(3)Se(2)O(12) (A=K, Rh, Cs, NH4): Hydrothermal synthesis in the V2O5-SeO2-AOH system and crystal structure of CsVSeO5

Hydrothermal reactions in the V2O5-SeO2-AOH systems (A = Na, K, Rb, Cs, NH4) were studied with various reagent mole ratios. Typical millimole ratios were V2O5/SeO2/AOH = 5 or 3/15/x in 10-mL aqueous solutions, where x was 5, 10, 15, and 20. The reactions with x = 5 for A = K, Rb, Cs, and NH4 at 230 degrees C produced single-phase products of the general formula AV(3)Se(2)O(12) With the (NH4)(VO)(3)(SeO3)(2) structure type. The x = 15 reactions for A = Rb and Cs yielded AVSeO(5) phases with a new structure type. The crystal structure for CsVSeO5 was determined with X-ray single-crystal diffraction techniques to be monoclinic (P2(1) (No. 4), a = 7.887(3) Angstrom, b = 7.843(2) Angstrom, c = 9.497(3) Angstrom, beta = 92.13(3)degrees, Z = 4). The structure of this compound consists of interwoven helixes extended in all three directions. The spires are composed of alternating SeO3 and VO5 units sharing common-edge oxygens in all three directions. For A = K and NH4, the reactions of this mole ratio did not produce any identifiable phases. Each of the compounds is characterized by powder X-ray diffraction, infrared spectroscopic, and thermogravimetric techniques. The dependency of the synthesis results on the reaction conditions is discussed and rationalized.