Octaaquabromouranium(IV) Tribromide Monohydrate, [UBr(H2O)8]Br3×H2O.

The cationic uranium complex, [U(H20)8Br] 3+, presents a tricapped trigonal prismatic structure in the solid state, with U--O distances (at T = 150 K) in the range 2.379 (8)-2.455 (8),~, and a U ~ B r bond length of 2.885 (2)A, in addition to an extended network of intermolecular hydrogen-bonding interactions. The title compound is the first octaaqua complex to be structurally characterized for an actinide element. The nine-coordinate complex [U(H:O)8Br]Br3.H20 displays a central U atom in direct contact with a Br ligand and the eight O atoms of eight water molecules. The overall geometry can be regarded as that of a tricapped trigonal prism, with 02, 04 and 07 capping the three rectangular faces O1/O3/O5/Brl, O1/O3/O6/O8 and O5/O6/O8/Brl, respectively (Fig. 1). The U--O bond distances [range 2.379 (8)-2.455 (8) ,~,] are similar to those observed in other aqua complexes of U Iv, 2.373 (12)-2.488 (6) ,~, (Haddad et at., 1987; Charpin et al., 1977), and rule out the presence of a dioxo (uranyl) complex, for which the characteristic U = O bond lengths are ca 1.76,~ (Rebizant et al., 1987;