Hydrothermal preparation of nickel(II)/uranium(IV) fluorides with one-, two-, and three-dimensional topologies

A modified compositional diagram for the reactions of Ni(C2H3O2)(2).4H(2)O with UO2(C2H3O2)(2).2H(2)O and HF in aqueous media under mild hydrothermal conditions (200 degreesC) has been completed to yield three Ni(II)/U(IV) fluorides, Ni-(H2O)(4)UF6.1.5H(2)O (1), Ni-2(H2O)(6)U3F16.3H(2)O (2), and Ni(H2O)(2)UF6(H2O) (3). The structure of I consists of one-dimensional columns constructed from two parallel chains of edge-sharing dodecahedral [UF8] units. The sides of the columns are terminated by octahedral Ni(II) units that occur as cis-[Ni(H2O)(4)F-2] polyhedra. In contrast, the crystal structure of 2 reveals a two-dimensional Ni(II)/U(IV) architecture built from edge-sharing tricapped trigonal prismatic [UF9] units. The top and bottom of the sheets are capped by fac-[Ni(H2O)(3)F-3] octahedra, The structure of 3 is formed from [UF8(H2O)] tricapped trigonal prisms that edge share with one another to form one-dimensional chains. These chains are then joined together into a three-dimensional network by corner sharing with trans-[Ni(H2O)(2)F-4] octahedra. Crystallographic data: 1, orthorhombic, space group Cmcm, a = 14.3383(8) Angstrom, b = 15,6867(8) Angstrom, c = 8,0282(4) A, Z = 8; 2, hexagonal, space group P6(3)/mmc, a = 7.9863(s) Angstrom, c = 16.566(1) Angstrom, Z = 2; 3, monoclinic, space group C2/c, a = 12.059(1) Angstrom, b = 6.8895(6) Angstrom, beta = 7.9351(7) Angstrom, beta = 92333(2)degrees, Z = 4.