Structure and stereochemistry in 'f-block' complexes of high coordination number. VI. Crystallographic characterizations of Bis[(1 ,1-dimethyl-3-oxobutyl)triphenyl-phosphonium] hexabromouranate(IV) and Tetrabromobis[ethane-1,2-diylbis(diphenylarsine) oxide]uranium(IV)

Abstract

Complexes obtained by the reaction of uranium pentabromide with triphenylphosphine and with ethane-1,2-diylbis(diphenylarsine) (Ph₂AsCH₂CH₂AsPh₂) have been characterized by single-crystal X-ray diffraction structure determination at 295 K and shown to be [Ph₃PCMe₂CH₂C(O)Me]_2- [Ubr₆](1) and [Ubr₄(Ph₂As(O)CH₂CH₂AsPh₂)₂] (2).

Crystals of (1) are orthorhombic, Pbca, a 20.46(1), b 16.033(8), c 15.663(10) Å, Z 4, the structure being refined to a residual of 0.07 for 990 independent reflections; in the centrosymmetric anion, U-Br distances range from 2.750(5) to 2.803(5) Å. Crystals of (2) are monoclinic, P2₁/c, a 12.64(1), b 10.870(6), c 20.81(2) Å, 110.88(2)º, Z 2, the structure being refined to a residual of 0.05 for 1531 independent reflections. In the centrosymmetric molecule, U-Br distances are 2.806(4) and 2.811(4) Å; the diarsine oxide ligand is unidentate, coordinated through the oxygen rather than the arsenic with U-O 2.19(1) Å.