[en] Valuable structural information, much of it unavailable by other methods, can be obtained about complexes in solution through NMR spectroscopy. From chemical shift and intensity measurements of complexed species, NMR can serve as a species-specific structural probe for molecules in solution and can be used to validate thermodynamic constants used in geochemical modeling. Fourier-transform nuclear magnetic resonance (FT-NMR) spectroscopy has been employed to study the speciation of uranium(VI) ions in aqueous carbonate solutions as a function of pH, ionic strength, carbonate concentration, uranium concentration, and temperature. Carbon-13 and oxygen-17 NMR spectroscopy were used to monitor the fractions, and hence thermodynamic binding constants of two different uranyl species U0₂(CO₃)₃^4- and (UO₂)₃(CO₃)₆^6- in aqueous solution. Synthetic buffer solutions were prepared under the ionic strength conditions used in the NMR studies in order to obtain an accurate measure of the hydrogen ion concentration, and a discussion of pH = -log(a_H⁺) versus p[H] = -log[H+] is provided. It is shown that for quantitative studies, the quantity p[H] needs to be used. Fourteen uranium(VI) binding constants recommended by the OECD NEA literature review were corrected to the ionic strengths employed in the NMR study using specific ion interaction theory (SIT), and the predicted species distributions were compared with the actual species observed by multinuclear NMR. Agreement between observed and predicted stability fields is excellent. This establishes the utility of multinuclear NMR as a species-specific tool for the study of the actinide carbonate complexation constants, and serves as a means for validating the recommendations provided by the OECD NEA

[en] A compound is described of the formula MX_nL_m wherein M is a metal atom selected from the group consisting of thorium, plutonium, neptunium or americium, X is a halide atom, n is an integer selected from the group of three or four, L is a coordinating ligand selected from the group consisting of aprotic Lewis bases having an oxygen-, nitrogen-, sulfur-, or phosphorus-donor, and m is an integer selected from the group of three or four for monodentate ligands or is the integer two for bidentate ligands, where the sum of n+m equals seven or eight for monodentate ligands or five or six for bidentate ligands. A compound of the formula MX_n wherein M, X, and n are as previously defined, and a process of preparing such actinide metal compounds are described including admixing the actinide metal in an aprotic Lewis base as a coordinating solvent in the presence of a halogen-containing oxidant

[en] The reaction of 1.4 equivalents of I₂ with Pu metal turnings in THF yields a bright orange, microcrystalline solid formulated as PuI₃(THF)₄. Analogous to UI₃(THF)₄ (D.L. Clark, S.G. Bott, R.N. Vrtis, A.P Sattelberger; Inorg. Chem. 1989, 28, in press; and references therein), the PuI₃(THF)₄ complex is a facile synthon in the preparation of a host of novel organometallic plutonium(III) complexes. Efforts towards the syntheses and characterization of these and other transuranic organometallic complexes are discussed

[en] The facile dissolution of neptunium or plutonium metal in coordinating solvents in the presence of 1.5 equiv. I₂ gives triiodide complexes as tetrasolvates, AnI₃(L)₄ (An = Np, 1a; Pu, 1b; L = solvent). The triiodide complexes are readily accessible precursors to a host of new transuranic compounds. The reaction of complexes 1a and 1b with 3 equiv. of NaN(SiMe₃)₂ gives the volatile amide complexes, An[N(SiMe₃)₂]₃ (An = Np, 2a; An = Pu, 2b). Treatment of 2a and 2b with 3 equiv. of 2,6-di-t-butylphenol (HOAr') gives the monomeric aryl oxide complexes, An(OAr')₃ (An = Np, 3a; An = Pu, 3b) which can then be reacted with 3 equiv. of LiCH(SiMe₃)₂ to give the alkyl complexes, An[CH(SiMe₃)₂]₃ (An = Np, 4a; An = Pu, 4b). The syntheses, and structural and spectroscopic characterization of these and other new transuranic complexes will be discussed

[en] This paper reports that neptunium and plutonium metal react cleanly with 1.5 equiv of I₂ in aprotic ligating solvents, L, to give the triiodide complexes as tetrasolvates, AnI₃L₄ [An is Np, L is tetrahydrofuran (THF) (1); An is Pu, L is THF (2a), pyridine (Py) (2b), and dimethyl sulfoxide (DMSO) (2c)]. These complexes are convenient precursors to both new and existing transuranium compounds. Reaction of the triiodide complexes 1 and 2a in hexane with 3 equiv of sodium bis(trimethylsilyl)amide provides the volatile, solvate-free tris (silylamide) complexes, An[N(SiMe₃)₂]₃ (An is Np, 3; An is Pu, 4). Hexan solutions of 3 and 4 react rapidly with 3 equiv of HO-2,6-(t-C₄H₉)₂C₆H₃ to give the aryloxide complexes An[O-26-(t-C₄H₉)₂C₆H₃]₃ (An is Np 5; An is Pu, 6). Preliminary investigations indicate that complexes 5 and 6 react with lithium bis(trimethylsilyl)methanide, Li[CH(SiMe₃)₂], in hexane to give the alkyl complexes An[CH(SiME₃)₂]₃ (An is Np, 7; An is PU, 8). Plutonium triiodide complex 2a readily reacts with LiC₅H₅ to give the known (n⁵-C₅H₅)₃Pu(THF). The homoleptic silylamide, aryloxide, and alkyl complexes are the first reported examples for transuranium elements

[en] The nonaqueous chemistry of trivalent neptunium and plutonium has been shown to closely mimic that of uranium(III). The organic-soluble actinide triiodide complexes AnI₃(THF)₄ (An = Np, Pu) are convenient precursors to a host of new transuranic complexes. Examples of new trivalent, homoleptic Np and Pu transuranic complexes include the previously reported coordinatively unsaturated tris(silylamides), An[N(SiMe₃)₂]₃, and the tris(aryloxides), An[0-2,6-(t-C₄H₉)₂C₆H₃]₃. Continued efforts in the syntheses and characterization by NMR, UV/Vis/NIR, and IR spectroscopy of new Np and Pu organometallic and alkoxide complexes are discussed

[en] The nitrate to thorium stoichiometry of the stable nitrate complexes of thorium, in an acetone/freon/water solvent mixture, has been studied by ¹⁵N nuclear magnetic resonance spectroscopy as a function of nitrate to thorium ratio at -100 degrees C. Thorium complexes incorporating one, two, four, and six nitrates are observed as the thorium to nitrate ratio increases. The trinitrato and pentanitrato complexes are not observed. The distribution of the complexes as a function of nitrate to thorium ratio are calculated using an equilibrium model

[en] The uranium(III) iodide complex UI₃(THF)₄ reacts cleanly at ambient temperature with 1 equiv of sodium and potassium pentamethylcyclopentadienide salts in tetrahydrofuran to form the mono-ring uranium(III) complex (η-C₅Me₅)UI₂(THF)₃(1). Additionally, reaction of UI₃(THF)₄ with 2 equiv or more of K(C₅Me₅) in THF solution leads to the formation of the bis-ring adduct (η-C₅Me₅)₂UI(THF) (2) in high yield. In the solid state 1 exhibits a pseudo-octahedral mer,trans ligand geometry with the C₅Me₅ ligand occupying one axial position. U-I bond lengths range from 3.161(1) to 3.179(1)angstrom, while U-O distances to the THF ligands lie in the range 2.496(8)-2.594(10)angstrom. 1 also provides a convenient entry into a variety of other mono-ring complexes of uranium(III). In the presence of excess pyridine, the coordinated THF ligands of 1 are readily displaced for form the tris(tyridine) adduct (η-C₅Me₅)UI₂(py)₃(3), which exhibits a mer,trans ligand geometry in the solid state similar to that of 1. Methathesis of the iodide ligands in 1 with 2 equiv of KN(SiMe₃)₂ affords the bis(amido) complex (η-C₅Me₅)U[N(SiMe₃)₂]₂(4). An X-ray diffraction study of this molecule reveals that methyl groups from both amido ligands are involved in agostic interactions with the uranium-(III) center

[en] Reaction of ThBr₄(THF)₄ in THF with one equivalent of cyclopentadienyl thallium, followed by three equivalents of KO-i-Pr, leads to the formation of the highly unusual hexanuclear complex [(η-C₅H₅)Th₂(O-i-Pr)₇]₃. A single crystal X-ray diffraction study revealed a cyclic structure in which three dinuclear [(η-₅H₅)Th₂(O-i-Pr)₇]₃ units are linked by (μ-η⁵:η⁵) bridging cyclopentadienyl groups. Th-C distances to the η-C₅H₅ ligands lie in the range 2.95 (2) to 3.02 (2) A, while terminal and bridging Th-O distances average 2.14 (2) and 2.41 (2) A, respectively. Crystal data for [η-C₅H₅)Th₂(O_iPr)₇]₃: Monoclinic space group C2/c, a =3D 30.853 (6), b =3D 17.765 (4), c =3D 20.858 (4) A, β 117.03 (3) deg, V =3D 10 183 A³, d_calc =3D 1.845 g cm^-3, Z =3D 4, R =3D 0.053, R_w =3D 0.067. (authors). 20 refs., 3 tabs., 1 fig

[en] Reaction of the mono-cyclopentadienyl uranium (III) complex (η-C₅Me₅) UI₂(THF)₃ (1) with one or two equivalents of carbon disulfide in toluene solution produces [(η-C₅Me₅)UI₂(THF)₃]₂S (2) in 60-80% yield. Compound 2 is converted to the trimetallic uranium (IV) cluster (η-C₅Me₅)₃U₃(μ₃-S) (μ₃-I)(μ₂-I)₃I₃ (3) in low yield upon standing in solution over a period of weeks. The solid state structure of 3 was determined, and if the η-C₅Me₅ ligand is considered to occupy a single coordination site, then the molecular structure of 3 can be viewed as a member of the well-known M₃(μ₃-X)₂(μ₂-X)₃X₆ structural type, with triply bridging sulfido and iodide ligands capping the triangular faces of the cluster. U-I, U-μ₂-I, and U-μ₃-I bond lengths average 2.952 (5), 3.096 (8), and 3.294 (5) A, respectively, while U-μ₃-S bond lengths average 2.75 (2) A. Crystal data for 3 (at - 171 deg C): Monoclinic space group P2₁/n, a =3D 12.224 (4), b =3D 17.098 (6), c =3D 21.631 (6) A, β 90.71 (1) deg, V =3D 4 520.82 A³, d_calc =3D 2.998 g cm^-3, Z =3D 4, R 0.089, R(w) 0.083. (authors). 58 refs., 3 tabs., 1 fig