Synthesis, structural study and thermal behaviour of a new compound: trirubidium bis(hydrogen sulphate) dihydrogen arsenate Rb3(HSO4)2.5(H2AsO4)0.5

Mixed crystals Rb-3(HSO4)(2.5)(H2AsO4)(0.5) have been prepared by slow evaporation from aqueous solution at room temperature. The crystals were characterized by X-ray single analysis, which revealed that Rb-3(HSO4)(2.5)(H2AsO4)(0.5) crystallizes in the space group P (1) over bar with lattice parameters: a = 7.471(3) angstrom; b = 7.636(1) angstrom; c = 12.193(2) angstrom; alpha = 71.91(1)degrees; beta = 73.04(6)degrees and gamma = 88.77(2)degrees. In this structure, the ordered S(1)O-4 and the disordered S(3)/AsO4 tetrahedra are connected by O-H center dot center dot O hydrogen bonds, to a zigzag chains running in the b-direction. These chains are, in turn, bonded to one another by disordered hydrogen bridges O-H center dot center dot H-O, to give a planar structure, with hydrogen-bonded sheets, laying parallel to (1 0 0). Each disordered tetrahedron is linked to a tetrahedron neighbouring S(2)O-4 by ordered hydrogen bonds. Broader peaks in IR spectrum of the title material support the assumption of disordered structure. Thermal analysis of the superprotonic transition in Rb-3(HSO4)(2.5)(H2AsO4)(0.5) showed that the transformation to the high-temperature phase occurs by one-step process at 404 K. Thermal decomposition of this compound takes place at much higher temperatures, with an onset of approximately 473 K.