THE CHEMISTRY OF URANIUM .41. COMPLEXES OF URANIUM TETRAHALIDE, WITH EMPHASIS ON IODIDE, AND TRIPHENYLPHOSPHINE OXIDE, TRIS(DIMETHYLAMINO)PHOSPHINE OXIDE OR TRIS(PYRROLIDINYL)PHOSPHINE OXIDE - CRYSTAL-STRUCTURE OF TETRABROMOBIS[TRIS(PYRROLIDINYL)PHOSPHINE OXIDE]URANIUM(IV)

The complexes UI4(tppo)2 (tppo = triphenylphosphine oxide), UI4(tdpo)2 (tdpo = tris(dimethylamino)phosphine oxide) and UI4(tpyrpo)2 (tpyrpo = tris(pyrrolidinyl)phosphine oxide) have been prepared and IR and electronic spectra of both the solid and solutions are reported for them. The crystal structure of UBr4(tpyrpo)2 has been determined by X-ray crystallography. The compound is monoclinic, space group C2/c, with a = 17.226(5), b = 11.883(5), c = 18.372(5) angstrom, beta = 109.30(3)-degrees; D(c) = 2.005(5) g cm-3. There are four molecules in the unit cell and the uranium atoms, which are trans-octahedrally surrounded by meridional bromide ions and apical oxygen atoms of the tpyrpo ligands, are in special positions on inversion centres. Selected bond lengths are: U-Br 2.775(2) angstrom, U-O 2.22(1) angstrom, P-O 1.52(1) angstrom, P-N 1.62(1) angstrom. The relative donor strengths of the three phosphine oxide ligands towards the uranium tetrahalides, as obtained from crystallographic data, are discussed. The preparation and characterization of the less common [UX3L3] complexes, where X = Cl, Br, I; Y = I, Ph4B; L = tdpo, tpyrpo and [UI(tdpo)5]I3 is discussed. Six coordinate chromophores are assigned to these complexes.