X-ray structural, vibrational and calorimetric studies of a new rubidium pentahydrogen arsenate RbH5(AsO4)(2)

Synthesis, crystal structure, Raman, IR and DSC characterization are given for a pentahydrogen arsenate of rubidium. X-ray investigations showed that the title compound (abbreviated RPA) crystallizes in an orthorhombic struct ure, space group Pbca and lattice parameters a = 7.9403(8) Angstrom, b = 9. 8218(6) Angstrom, c = 20.4244(6) Angstrom, V = 1592.9(2) Angstrom (3), Z = 8 and rho (cal) = 3.072 g cm(-3). The structure was solved from 1568 indepe ndent reflections With R-1 = 0.047 and WR2 = 0.067, refilled with 106 param eters. The structure is different from RbH5(PO4)(2) (abbreviated RPP). It c an be regarded as consisting of isolated AsO4 tetrahedra connected by stron g H-bonds [2.432(6)-2.638(6) Angstrom] to on infinite network. The AsO43- g roups are located in layers parallel to the ab plane, and interleaved rubid ium cations ensure cohesion between the sheets. The short hydrogen bond [2. 432(6) Angstrom] is probably not symmetric. The Raman and infrared spectra at room temperature were investigated in the frequency ranges 15-1000 and 2 50-4000 cm(-1), respectively. An assignment of all the bands is given. Diff erential scanning calorimetry showed that RPA crystals do not exhibit any p hase transition in the range 100-575 K, (C) 2001 Elsevier Science B.V. All rights reserved.