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)2·4H2O with UO2(C2H3O2)2·2H2O and HF in aqueous media under mild hydrothermal conditions (200 °C) has been completed to yield three Ni(II)/U(IV) fluorides, Ni(H2O)4UF6·1.5H2O (1), Ni2(H2O)6U3F16·3H2O (2), and Ni(H2O)2UF6(H2O) (3). The structure of 1 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)4F2] 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)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) Å, b = 15.6867(8) Å, c = 8.0282(4) Å, Z = 8; 2, hexagonal, space group P63/mmc, a = 7.9863(5) Å, c = 16.566(1) Å, Z = 2; 3, monoclinic, space group C2/c, a = 12.059(1) Å, b = 6.8895(6) Å, c = 7.9351(7) Å, β = 92.833(2)°, Z = 4.