J. Marçalo

Some reactions of hydrotris(3,5-dimethylpyrazolyl)-borato trichloroactinides(IV), MCl3(HBL3)·THF (M ≡ ThIV, UIV; L ≡ 3,5-dimethylpyrazolyl, THF ≡ tetrahydrofuran)☆

Abstract The thorium(IV) and uranium(IV) compounds MCl2(Cp)(HBL3) (Cp ≡ η5-C5H5), MCl2[N(SiMe3)2](HBL3) and M(NPh2)3(HBL3) have been prepared from MCl3(HBL3)·THF. IR, near-IR-visible, 1H NMR and 11B NMR spectra are reported for these compounds.

Alkoxide and aryloxide derivatives of actinide(IV) polypyrazolylborates. Part II. Uranium(IV) bis[hydrotris(pyrazol-1-yl)borate] complexes

Abstract The complexes U(HBpz 3 ) 2 (OR) x Cl 2− x (pz=pyrazol- 1-yl; x =1, 2; RBu t , Pr i , and C 6 H 2 -2,4,6- Me 3 ) have been prepared from the reaction of U(HBpz 3 ) 2 Cl 2 with sodium alkoxides and aryloxides in the ratio 1:1 and 1:2. The temperature dependence of the 1 H NMR of the complexes has been studied. Fluxional behaviour was observed for the poly(pyrazol-1-yl)borate ligands and the barrier to rotation about the U-B axis was estimated for the complexes U(HBpz 3 ) 2 (OBu t ) 2 (Δ G ‡=53 ± 4 kJ mol −1 and U(HBpz 3 ) 2 (OC 6 H 2 -2,4,6-Me 3 )Cl (Δ G ‡=39 ± 3 kJ mol −1 ). 1 H NMR studies also indicated restricted rotation about the UOR bonds in the complexes U(HBpz 3 ) 2 (OR)Cl (Δ G ‡=62 ± 5 kJ mol −1 and U(HBpz 3 ) 2 (OR) 2 (Δ G ‡=62 ± 4 kJ mol −1 with RC 6 H 2 -2,4,6-Me 3 .

Actinide poly(pyrazol-1-yl)borate complexes: Synthesis and characterization of hydrotris(3,5-dimethylpyrazol-1-yl) borate actinide(IV) aryloxides

Abstract Reactions of MCl3[HB(3,5-Me2Pz)3](thf) [M  Th(IV), U(IV)] with NaOAr (Ar  C6H5, C6H2-2,3,5-Me3) in thf yielded the complexes MCl3 − x(OAr)x[HB(3,5-Me2Pz)3](thf)y (x = 1–3; y = 0, 1) which were characterized by IR, near-IR-visible, and 1H-NMR spectroscopies. The single crystal X-ray structure of UCl(OC6H5)2 [HB(3,5-Me2Pz)3](thf) was determined. The uranium centre is seven-coordinate and displays capped octahedral geometry. This structure is compared with the previously reported structure of UCl3[HB(3,5-Me2Pz)3](thf).

Thorium and Uranium Carbide Cluster Cations in the Gas Phase: Similarities and Differences between Thorium and Uranium

Laser ionization of AnC4 alloys (An = Th, U) yielded gas-phase molecular thorium and uranium carbide cluster cations of composition An(m)C(n)(+), with m = 1, n = 2-14, and m = 2, n = 3-18, as detected by Fourier transform ion-cyclotron-resonance mass spectrometry. In the case of thorium, Th(m)C(n)(+) cluster ions with m = 3-13 and n = 5-30 were also produced, with an intriguing high intensity of Th13C(n)(+) cations. The AnC13(+) ions also exhibited an unexpectedly high abundance, in contrast to the gradual decrease in the intensity of other AnC(n)(+) ions with increasing values of n. High abundances of AnC2(+) and AnC4(+) ions are consistent with enhanced stability due to strong metal-C2 bonds. Among the most abundant bimetallic ions was Th2C3(+) for thorium; in contrast, U2C4(+) was the most intense bimetallic for uranium, with essentially no U2C3(+) appearing. Density functional theory computations were performed to illuminate this distinction between thorium and uranium. The computational results revealed structural and energetic disparities for the An2C3(+) and An2C4(+) cluster ions, which elucidate the observed differing abundances of the bimetallic carbide ions. Particularly noteworthy is that the Th atoms are essentially equivalent in Th2C3(+), whereas there is a large asymmetry between the U atoms in U2C3(+).

Alkoxide and aryloxide derivatives of actinide(IV) polypyrazolylborates. Part I. Uranium(IV) and thorium(IV) hydrotris(3,5-dimethylpyrazol-1-yl)borate complexes

Abstract A series of complexes of the type M[HB(3,5- Me2pz)3](OR)xCl3−x (with RPri, But, C6H22,4,6- Me3; x=1, MU(IV); x=2, MU(IV), Th(IV); x=3, MU(IV), Th(IV)) have been prepared from M[HB(3,5-Me2pz)3]Cl3(THF) and characterized by IR, near IRVis, and 1H NMR spectroscopy. Variable temperature 1H NMR studies of the uranium compounds indicated restricted rotation of the OR groups; values of ΔG‡ for the rotation about the UOR bonds were estimated for the complexes U[HB(3,5- Me2pz)3](OC6H2-2,4,6-Me3)Cl2 (ΔG‡=49 ± 4 kJ mol−1), and U[HB(3,5-Me2pz)3](OC6H2-2,4,6- Me3)2Cl(ΔG‡=41 ± 3 kJ mol−1).

Oxo-Exchange of Gas-Phase Uranyl, Neptunyl, and Plutonyl with Water and Methanol

A challenge in actinide chemistry is activation of the strong bonds in the actinyl ions, AnO2(+) and AnO2(2+), where An = U, Np, or Pu. Actinyl activation in oxo-exchange with water in solution is well established, but the exchange mechanisms are unknown. Gas-phase actinyl oxo-exchange is a means to probe these processes in detail for simple systems, which are amenable to computational modeling. Gas-phase exchange reactions of UO2(+), NpO2(+), PuO2(+), and UO2(2+) with water and methanol were studied by experiment and density functional theory (DFT); reported for the first time are experimental results for UO2(2+) and for methanol exchange, as well as exchange rate constants. Key findings are faster exchange of UO2(2+) versus UO2(+) and faster exchange with methanol versus water; faster exchange of UO2(+) versus PuO2(+) was quantified. Computed potential energy profiles (PEPs) are in accord with the observed kinetics, validating the utility of DFT to model these exchange processes. The seemingly enigmatic result of faster exchange for uranyl, which has the strongest oxo-bonds, may reflect reduced covalency in uranyl as compared with plutonyl.

Preparation of dense 13C pellets using spark plasma sintering technique

Abstract Dense 13C pellets were prepared using the spark plasma sintering (SPS) technique. 13C material was used as starting powders with fibre-like shape and heterogeneous fibre diameters of few nanometres to few hundred nanometres. Graphite die and punches were used as a container, and the 13C powder was isolated from both die and punches with pure flexible graphite papyex. Results show that densification starts at 1900°C when the pressure overpasses 60 MPa, and maximum effect has been obtained at the same temperature <80 MPa. The powders were densified to more than ∼90% of the theoretical density by the SPS process. Such 13C pellets are of special interest to prepare actinide or lanthanide carbide intermetallics for spectroscopy studies.

Evidence for cathodic electrodeposition of radon species

Evidence for the cathodic deposition of222Rn was given in experiments involving the electrodeposition of226Ra and its daughters from an ethanolic solution slightly acidified with hydrogen fluoride. The presence of silicate ions was found to be essential for the radon deposition to take place.