STRUCTURAL PHASE-TRANSITIONS AND VIBRATIONAL STUDY OF CSH(SO4)(0.76)(SEO4)(0.24)

CsH(SO4)(0.76)(SeO4)(0.24), M(m) = 241.2, single crystals were grown a nd appear to be isomorphous with CsHSeO4. The space group is P2(1)/a, the lattice constants are: a = 7.8340(10) Angstrom. b = 8.2147(6) Angs trom, c = 7.4410(10) Angstrom beta = 110.910(10)degrees V = 447.50(9) Angstrom(3), Z = 4, D-x = 3.582 Mg m(-3), lambda(MoK alpha) = 0.71069 Angstrom, mu(MoKalpha) = 10.269 mm(-1) F(000) = 818, T = 293(2) K (roo m temperature phase), R = 0.023 and wR = 0.0563 for 883 observed refle ctions. The hydrogen sulphate or hydrogen selenate groups are connecte d by hydrogen bonds. The separated chains of asymmetric hydrogen bonds run parallel to the c-axis. The O-H...O distance utilized in the hydr ogen bonding is 2.608 Angstrom which is 2.603 Angstrom for CsHSeO4. Mi xed cesium hydrogen sulphate selenate CsH(SO4)(0.76)(SeO4)(0.24) under goes two phase transitions at T = 333 and 408 K. The values of the ent halpies are 2.02 and 4.37 kJ/mol, respectively.