Hydrothermal Preparation of Nickel(ll)/Uranium(IV) Fluorides with One-, Two-, and Three-Dimensional Topologies

A modified compositional diagram for the reactions of Ni(C2H3O2)2 with UO2(C2H3O2)2*2H2O and HF in aqueous media under mild hydrothermal conditions (200 °C) has been completed to yield three Ni(ll)/U(IV) fluorides, Ni(H2O)4UF6-1.5H20 (1), Ni2(H2O)6U3F16.3H2O (2), and Ni(H2O)2UF6(H2O) (3). The structure of 1 consists of onedimensional columns constructed from two parallel chains of edge-sharing dodecahedral [UF8] units. The sides of the columns are terminated by octahedral Ni(ll) units that occur as cis-[Ni(H2O)4F2] polyhedra. In contrast, the crystal structure of 2 reveals a two-dimensional Ni(ll)/U(IV) architecture built from edge-sharing tricapped trigonal prismatic [UF9] units. The top and bottom of the sheets are capped by /ac-[Ni(H20)3F3] 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)2F4] octahedra. Crystallographic data: 1, orthorhombic, space group Cmcm, a = 14.3383(8) A, b = 15.6867(8) A, c •= 8.0282(4) A, Z= 8; 2, hexagonal, space group PG^mmc, a = 7.9863(5) A, c = 16.566(1) A, Z = 2; 3, monoclinic, space group C2/c, a = 12.059(1) A, b = 6.8895(6) A, c = 7.9351(7) A, ft = 92.833(2)°, Z = 4.