INTERACTION BETWEEN URANIUM(V) AND URANIUM-(VI) FLUORIDES AND NITROGEN BASES - CHARACTERIZATION AND CRYSTAL-STRUCTURES OF THE DIMORPHIC ADDUCT UF5-CENTER-DOT-BIPY (BIPY=2,2'-BIPYRIDYL)

The interaction between UF6 or UF5 and 2-fluoropyridine (F-py) or 2,2'-bipyridyl (bipy) has been investigated in view of obtaining new adducts of these fluorides. In CH2Cl2 solution, UF6 reacts with F-py and bipy to yield UF4.F-py and U2F12.bipy, respectively. However, for the UF6/bipy system, the reduction of UF6 by bipy is the dominant process, and the formation of U2F12.bipy might be a preliminary step of this reduction. The reaction of beta-UF5 with F-py does not lead to a crystallized compound, whereas, with bipy, the dimorphic adduct UF5 bipy and the ionic derivative [(bipy)2H](+)[UF6](-) are obtained. All these compounds but UF4.F-py are moisture sensitive. The adduct of UF5 has been characterized by elemental analyses, X-ray powder data, and infrared spectroscopy. Solutions of this adduct in CD3CN were studied by NMR spectroscopy. The crystal structures of the two forms of UF5.bipy have been determined by X-ray diffraction methods. In both forms the coordination polyhedron of the uranium atom is a distorted monocapped trigonal prism made up of five fluorine atoms and two nitrogen atoms of the bipyridine ligand. The molecular unit, however, has a different local symmetry in the two forms. The space groups, unit cell parameters, and R factors are as follows: UF5.bipy (I), monoclinic, C2/c (No. 15), 7.086(3) Angstrom, b = 14.443(3) Angstrom, c = 11.501(3) Angstrom, beta = 99.79 (3)degrees, V = 1160.0 (9) Angstrom(3), Z = 4, R = 0.028; UF5.bipy (II), orthorhombic, Pnma (No. 62), a = 9.731(3) Angstrom, b = 6.933(6) Angstrom, c = 17.729(5) Angstrom, V = 1196(2) Angstrom(3), Z = 4, R = 0.022.