Ben Zeelie

The chemistry of uranium. Part 35. Synthesis and characterization of UI4L2 complexes (L = bulky amide ligands) and the crystal structure of UI4tmu2 (tmu = tetramethylurea)

Abstract A number of trans-octahedral complexes of uranium tetraiodide have been isolated for the first time using bulky CO amide ligands. The solid reflectance electronic spectra of these complexes indicated a shift in the major peaks of their spectra to higher energies with reference to the of UI62−. The infrared spectra of the substituted complexes showed a reverse of the position of the CO stretching frequencies and the NCN stretching frequencies upon complexation, indicating the high Lewis acidity of UI4. The structure of UI4tmu2 has been determined by X-ray crystallography. The compound crystallized in the orthorhombic system, space group Pbcn. Cell constants are: a = 11.480(5), b = 14.657(5), c = 13.453(5) A; Dc = 2.87 g cm−3. There are four independent molecules of the compound in the unit cell with uranium, oxygens and their attached carbon atoms lying on the two-fold symmetry axis. The uranium atom is trans-octahedrally surrounded by meridional iodide ions and apical oxygen atoms of tmu groups. The OUO sequency is linear. Selected mean bond lengths are: UI 3.01 A, UO 2.185 A, CO 1.29 A. A comparison was made between the UX4tmu2 structures (X = Cl, Br and I). UI4tmu2 proved to be much more thermally unstable than its chloro and bromo analogues.

The Chemistry of Uranium. Part 34. Structural and Thermal Properties of UX4L2 Complexes (X Cl and Br; L = N,N,N′,N′-Tetramethylurea)

Abstract The crystal structure of the isomorphous pair UX4L2 has been determined by X-ray crystallography. The compounds crystallize in the triclinic system, space group P 1 . Cell constants are: UCl4L2, a=15.061(5), b=9.255(4), c=8.515(4) A, α=62.S7(3), β=106.50(3), γ=98.86(3)o; UBr4L2, a=15.413(5), b=9.443(3), c=8.710(4) A, α=62.58(3), β=106.40(3), γ=99.76(3)o. Density values are 2.01 g cmt−3 for UCl4l2 and 2.43 g cmt−3 for UBr4L2. There are two independent molecules of the compound in the unit cell, with the uranium atoms on the inversion centres at the origin and at the centre of the cell. Structural details in the isomorphous compounds are fully comparable. Selected bond lengths are: UCl(mean) 2.62 A, UBr(mean) 2.78 A, UO(mean) 2.22 A (chloride) and 2.21 A (bromide). The uranium atom is six-coordinated octahedral. IR spectra data are reported. It is indicated that the CO vibration of the ligand is greatly lowered upon complexation and the antisymmetric NCN stretching vibration highered to the extent that these interchange in terms of their relative positions in the free ligand. The CO peaks are fairly broad in the complexes which is in agreement with the two independent molecules in the unit cell. Thermal degradation studies in a nitrogen atmosphere were done and oxygen abstraction of the ligand by uranium(IV) occurred, resulting in the formation of UO2. Two stable intermediates could be isolated from the UCl4tmu2, viz. UOCl2tmu and UO2Cl. This method thus produced a convenient method of preparation of the latter compound.

The chemistry of uranium. Part 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)

Abstract 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) A, β=109.30(3)°; Dc=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) A, UO 2.22(1) A, PO 1.52(1) A, PN 1.62(1) A. 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.

Structural configuration of hexamethylphosphoramide complexes of uranium tetrahalides by magnetic susceptibility

Magnetic susceptibilities of UX4hmpa2 (where X = Cl−, Br− and I−; hmpa = hexamethylphosphoramide) were measured from the b.p. of liquid helium to room temperature. The temperature dependence of the magnetic susceptibilities indicates that UI4hmpa2 has a trans-configuration, as have UCl4hmpa2 and UBr4hmpa2. Analysis of the magnetic susceptibilities on the basis of the ligand-field theory shows the distortion of the ligand field around the central uranium ion from Oh symmetry in the following order: UCl4hmpa2 < UBr4hmpa2 < UI4hmpa2.

The chemistry of uranium. Part 38. The interaction of UI4 with sulphoxide ligands and the use of dimethyl sulphoxide as oxidizing agent in the preparation of UO2I2 complexes

Abstract The reactions of UI4 with a number of sulphoxide donor ligands have been studied in non-aqueous media and compared to the behaviour of UCl4 and UBr4 in the presence of these ligands. UI4 is readily oxidized by dmso (dimethyl sulphoxide) and dibso (di-isobutyl sulphoxide) at room temperature and the only stable complexes isolated were UI4(dmso)8 and UI4 (dibso)6. The large tbso (di-tertiarybutyl sulphoxide) gives stable, bis-complexes, UX4L2 for all three halides. The oxidation of UI4 by dmso in ethyl acetate provides a relatively easy and reliable method for the preparation of uranyl iodide complexes, e.g. UO2I4A2 (A = Ph4P+, Ph4As+, etc.), UO2I2L2 (L = triphenylarsine oxide (tpao), tris- (dimethylamino)phosphine oxide (tdpo), N,N′- dimethylpropylene urea (dmpu), N,N,N′,N′-tetra- methylurea (tmu) and N,N′-dimethylethylene urea (dmeu) and UO2I2L4 where L = tdpo and tpao.

The chemistry of uranium. Part 36. Synthesis and characterization of some novel triphenylarsine oxide complexes of UI4

Abstract The reaction between UI 4 and triphenylarsine oxide (tpao) has been studied in non-aqueous solution. A number of solid complexes have been isolated, viz. α-UI 4 tpao 2 , β-UI 4 tpao 2 , UI 4 tpao 4 and UI 4 tpao 6 . The room temperature stable UI 4 tpao 2 (α form) proved not to be the trans -octahedral species as commonly found for UCl 4 and UBr 4 , but an auto- ionized solid, viz. [UI 2 tpao 4 ] [UI 6 ]. The properties of these species are discussed and compared to their chloro- and bromo-analogues.

New uranium tetraiodide complexes

A new type of uranium tetraiodide complex, viz. Ul4L2(where L = a bulky amide or phosphine oxide ligand) and new suitable starting materials for the preparation of uranium(IV) iodo-complexes have been prepared.

Di-iodotetrakis(triphenylarsine oxide)uranium(IV) hexaiodouranate(IV). A new type of actinoid co-ordination compound

A new type of co-ordination compound having UX4L2 stoicheiometry consisting of both cationic and anionic six co-ordinated metal species has been isolated (M = uranium, X = iodide, and L = neutral donor ligand).