SYNTHESIS, CRYSTAL-STRUCTURE, AND THERMAL-BEHAVIOR OF CERIUM(IV) OXIDE NITRATE CE2O(NO3)(6)(H2O)(6)CENTER-DOT-2H2O

A new cerium(IV) oxide nitrate, Ce2O(NO3)(6)(H2O)(6).2H(2)O, was synth esized from the dissolution in nitric acid of hydrous ceria with high specific area. Its crystal structure was determined from three-dimensi onal X-ray diffraction data. Crystals are monoclinic, space group P2(1 )/c, with a = 8.7233(8), b = 8.9397(8), c 13.981.(1) Angstrom, beta = 94.909(7)degrees, and Z = 2. Full matrix least-squares techniques led to a conventional R factor of 0.023 for 2091 observed reflections. The structure consists of dimer units with formula Ce2O (NO3)(6)(H2O)(6), which are formed by two equivalent 10-fold cerium(IV) polyhedra conne cted by an oxo bridge. Additional water molecules are located between these units. Hydrogen bonds ensure the continuity of the structure, Th e thermal decomposition under vacuum of this compound was investigated by means of sequential thermodiffractometry. Two new phases, Ce-2 O(N O3)(6).3H(2)O and Ce2O(NO3)(6) were identified and finely dispersed Ce O2 powder was obtained at low temperature (180 degrees C). The microst ructural features of the oxide annealed at 600 degrees C were also stu died, showing the ''isotropic'' shape of the crystallites. (C) 1994 Ac ademic Press, Inc.