[en] New mono pentamethylcyclopentadienyl thorium complexes Cp*Th(OAr)2Me and Cp*Th(OAr)(CH2SiMe3)2 were synthesized with the later complex being crystallographically characterized (OAr = 2,6-di-^tButylphenol). The stability and reactivity of these alkyl complexes will be explored. In addition, mono Cp* thorium complexes were synthesized by reaction of Cp* with a thorium amide complex and the product and mechanism of the reaction will be discussed

[en] Extensive synchrotron (28 K) and conventional sealed-tube (9 K) X-ray diffraction data have been collected on Th(S₂PMe₂)₄. Modeling of the electron density of the complex shows the bonding is quite ionic with little diffuse f or d type bonding density. Furthermore a large polarization of the Th core is observed revealing some 5d-like involvement in the bonding. High-quality ab initio density functional calculations are not able to reproduce these features and instead predict rather covalent bonding with considerable 6d-5f mixing. The study suggests that this theoretical method exaggerates the covalent nature of actinide bonds. It is shown that the most direct measure of covalence -- charge transfer and electron distributions -- can be usefully estimated by X-ray diffraction even in this most unfavorable of cases, where many actinide core electrons are present. The use of very low temperature data is crucial in the study of heavy metal complexes in order to minimize systematic errors such as thermal diffuse scattering and anharmonicity. The fact that accurate synchrotron radiation diffraction data can be measured within days makes studies of compounds beyond the first transition series more frequently within reach

[en] The mono- and bisalkoxide uranium complexes U(BH₄)₃(OCHR¹R²)(THF)₂ 1 and U(BH₄)₂(OCHR¹R²)₂(THF)₂ 2 were prepared successively in tetrahydrofuran (THF) by treatment of U(BH₄)₄ with the corresponding ketone R¹R²C = O (acetone, benzophenone, cyclohexanone, 2-methylcyclohexanone, 4-tert-butylcyclohexanone, and norcamphor). The borane BH₃.THF was liberated during the formation of 1 and 2, and reacted with the ketone to give the alkoxyborane species B(OCHR¹R²)_nH_3-n. Formation of 1 also resulted from: a) reaction of U-BH₄)₄ with the alkoxyborane species; b) reaction of U(BH₄)₄ with 2; and c) reaction of 2 with BH₃.THF. The alkoxide groups of 1 and 2 rapidly exchange with those of the alkoxyborane species. The uranium complexes 1 and alkoxyborane species resulting from the reaction of U(BH₄)₄ with the substituted cyclohexanones or norcamphor have been separated and their hydrolysis afforded the corresponding epimeric alcohols in different proportions. The monoalkoxide compounds 1 were alternatively prepared by reaction of the ketones R¹R²C = O with UCl₄ in the presence of LiBH₄ or by treatment of U(BH₄)₄ with the alcohols R¹R²CHOH. The octahedral crystal structures of U(BH₄)₃(OCHPh₂)(THF)₂ 1b and U(BH₄)₂(OCHPh₂)₂(THF)₂ 2b show that in 1b, the two equatorial THF ligands (and the two equatorial BH₄ groups) are in relative cis positions whereas they are trans in 2b

[en] The [(UO₂)₂F₆-2H₂O]^2- ion has been observed in the Cs₂[(UO₂)2F₆-2H₂O] compound. It is similar to the (UO₂)₂F₈^4- ion already found in the Cs₄(UO₂)₂F₈-2H₂) and Rb₄(UO₂)₂F₈-2H₂O complexes in which two of the fluorine atoms are replaced by two water molecules. Because of the existence of hydrogen bonds, these ions group themselves together in this structure to form chains

[en] The application of crystal field and molecular orbital theory to an octahedrally coordinated f¹ system is reviewed. The optical and magnetic data available for UX₆^- (X=F, Cl, Br) complexes are analyzed in terms of these theories. It is shown the usual approximation for the orbital reduction factors, is not meaningful for UX₆- (X=Cl, Br). The orbital reduction factors are evaluated for each UX₆^- complex and their values are correlated with an increase in covalency in the UX₆^- complexes as X changes from F to Br

[en] An extended MM3 model has been used to identify all low energy configurations for U(IV) complexes with catecholate and aquo ligands. Both stochastic and systematic conformational analyses of[U(cat)n(OH2)8-n]4-2n complexes, n= 1 - 4, establish that 20 of the 67 possible stereochemistries are minima on the MM3 potential surface. The stable stereochemistries are reported for each stoichiometry and, where possible, the results are compared with experimental data and with the predictions from prior repulsion energy calculations

No abstract available

[en] Preliminary calculation was made for the equilibrium constant of the exchange reaction of uranium isotopes between uranous and uranyl ions by taking only the hydration of uranous ions in consideration. The reduced partition function ratio of uranous complexes was calculated by using the formula of J. Bigeleisen et al. and also Badger's empirical relation of stretching force constant. The equilibrium constants of the following two reactions are plotted as functions of the distance between uranous ion and the coordinated water; ²³⁵U(H₂O)₈⁴⁺ + ²³⁸UO₂²⁺ = ²³⁸U(H₂O)₈⁴⁺ + ²³⁵UO₂²⁺, ²³⁵UCl₄(H₂O)₄ + ²³⁸UO₂²⁺ = ²³⁸UCl₄(H₂O)₄ + ²³⁵UO₂²⁺. The figures indicate that at 20⁰C, uranium-235 is expected to concentrate in the uranyl ions if the bond length between the uranous ion and the coordinated water is less than 2.26A and 2.30A respectively in the above described two reactions. So it is concluded that uranium-235 can be expected to concentrate in uranyl ions due to the effect of the hydration of uranous ions, and the other complex formation of uranous ions also has the same effect. (Yamanouchi, S.)

No abstract available

[en] The paper presents the synthesis, chemical properties and X-ray powder diffraction data as well as magnetic and spectroscopic properties of a number of new uranium(III) complex compounds of the formulas [(C₂H₅)₄N]₃U(NCS)₆, [(CH₃)₄ N]₃ UCl₆ and [(CH₃)₃ N(CH₂)₆ N(CH₃)₃]₂ UCl₅. Magnetic susceptibilities of polycrystalline samples of the compounds were measured by the Faraday method in the 6.2--300K range. The IR and UV-VIS spectra were recorded in the 80--4,000 and 4,000--30,000 cm^-1 spectral ranges, respectively and discussed