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1.
Dalton Trans ; 2020 May 08.
Artigo em Inglês | MEDLINE | ID: mdl-32383725

RESUMO

The neptunyl (Np(v)O2+/Np(vi)O22+) cation is the dominant form of 237Np in acidic aqueous solutions and the stability of the Np(v) and Np(vi) species is driven by the specific chemical constituents present in the system. Hydrogen bonding with the oxo group may impact the stability of these species, but there is limited understanding of how these intermolecular interactions influence the behavior of both solution and solid-state species. In the current study, we systematically evaluate the interactions between the neptunyl tetrachloride species and hydrogen donors in coordination complexes and in the related aqueous solutions. Both Np(v) compounds (N2C4H12)2[Np(v)O2Cl4]Cl (Np(V)pipz) and (NOC4H10)3[Np(v)O2Cl4] (Np(V)morph) exhibit directional hydrogen bonding to the neptunyl oxo group while Np(vi) compounds (NC5H6)2[Np(vi)O2Cl4] (Np(VI)pyr) and (NOC4H10)4[Np(vi)O2Cl4]·2Cl (Np(VI)morph) assemble via halogen interactions. The Raman spectra of the solid-state phases indicate the activation of vibrational bands when there is asymmetry of the neptunyl bond, while these spectral features are not observed within the related solution phase spectra. Density functional theory calculations of the Np(V)pipz system suggest that activation of the ν3 asymmetric stretch and other combination modes lead to additional complexity within the solid-state spectra. Electrochemical analyses of complexes in the solution phases are consistent with the results of the crystallization experiments as the voltammetric potentials of Np(v)/Np(vi) complexes in the presence of protonated heterocycles differ from the potentials of pure Np(v) and may correlate with the hydrogen bonding interactions.

2.
Chem Commun (Camb) ; 55(63): 9319-9322, 2019 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-31313772

RESUMO

Crown-ether molecules are used in radiochemical separations due to their high selectivity for a range of metal cations. Previous investigations regarding the interactions of 18-crown-6 (18C6) with 237Np suggested the formation of a Np(v) inclusion complex, but also reported rapid reduction of Np(vi) to Np(v) in the presence of the ether molecule. Herein, we investigate the impact of crown ether functionalization by exploring the Np(v) and Np(vi) dicyclohexano-18-crown-6 (DCH-18C6) systems. Two [X(DCH-18C6)]2[Np(vi)O2Cl4] compounds (X = K (1) and Na (2)) were crystallized and characterized by single crystal X-ray diffraction and Raman spectroscopy. Additional studies of Np(vi), Np(v), and Np(v)/Np(vi) in solution indicated redox stability in the presence of functionalized crowns and preferential crystallization of Np(vi) DCH-18C6 solids. These results indicate that functionalization of the crown can lead to higher resistance to radiolysis and increased stability of the Np(vi) oxidation state in solution.

3.
Dalton Trans ; 48(24): 8861-8871, 2019 Jun 28.
Artigo em Inglês | MEDLINE | ID: mdl-31139781

RESUMO

The interaction of the actinyl (AnO22+) oxo group with low-valent cations influences the chemical and physical properties of hexavalent actinides, but the impact of these intermolecular interactions on the actinyl bond and their occurrence in solution and solid state phases remain unclear. In this study, we explore the coordination of alkali cations (Li+, Na+, K+) with the [NpO2Cl4]2- coordination complexes using single-crystal X-ray diffraction, Raman spectroscopy, and density functional theory (DFT) calculations and compare to the related uranyl system. Three solid-state coordination compounds ([Li(12-crown-4)]2[NpO2Cl4] (LiNp), [Na(18-crown-6)H2O]2[NpO2Cl4] (NaNp), and [K(18-crown-6)]2[NpO2Cl4] (KNp) have been synthesized and characterized using single-crystal X-ray diffraction and Raman spectroscopy. Only Li+ cations interact with the neptunyl oxo in the solid-state compounds and this results in a red-shift of the NpO22+ symmetric stretch (ν1). Raman spectra of Np(vi) solutions containing lower Li+ concentrations display a single peak at ∼854 cm-1 and increasing the amount of Li+ results in the ingrowth of a second band at 807 cm-1. DFT calculations and vibrational analysis indicate the lower frequency vibrational band is the result of interactions between the Li+ cation and the neptunyl oxo. Comparison to the related uranyl system shows similar interactions occur in the solid state, but subtle differences in the actinyl-cation modes in solution phase.

4.
Chem Commun (Camb) ; 54(76): 10698-10701, 2018 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-30187044

RESUMO

Oxo group activation with reduction of neptunyl(vi) and plutonyl(vi) to tetravalent hydroxo species by the hydroxypyridinone siderophore derivative 3,4,3-LI-(1,2-HOPO) was investigated in the gas-phase via electrospray ionization mass spectrometry, in solution via Raman spectroscopy, and computationally via density functional theory. Dissociation of the gas-phase tetravalent complexes resulted in actinide-hydroxo bond cleavage.

5.
Chem Commun (Camb) ; 54(77): 10828-10831, 2018 Sep 25.
Artigo em Inglês | MEDLINE | ID: mdl-30137085

RESUMO

Physical properties of actinyl materials are influenced by the presence of oxo functional groups. Herein, we report large thermal expansion coefficients for a uranyl metal organic nanotube that switch from positive to negative upon dehydration. Different behaviour is observed in the neptunyl system due to variations in the oxo interactions.

6.
Acta Crystallogr C Struct Chem ; 73(Pt 8): 588-592, 2017 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-28776508

RESUMO

The crystal structures of two new bimetallic uranyl-transition metal compounds with diglycolic acid [or 2-(carboxymethoxy)acetic acid] have been hydrothermally synthesized and structurally characterized via single-crystal X-ray diffraction. The compounds, namely catena-poly[[[tetraaquamanganese(II)]-µ-2,2'-oxydiacetato-[dioxidouranium(VI)]-µ-2,2'-oxydiacetato] dihydrate], {[MnU(C4H4O5)2O2(H2O)4]·2H2O}n, and catena-poly[[[tetraaquacobalt(II)]-µ-2,2'-oxydiacetato-[dioxidouranium(VI)]-µ-2,2'-oxydiacetato] dihydrate], {[CoU(C4H4O5)2O2(H2O)4]·2H2O}n, both crystallize in the triclinic space group P-1. These compounds form one-dimensional chains via alternating uranyl and transition metal building units. The chains then assemble into three-dimensional supramolecular networks through several hydrogen bonds between water molecules and diglycolate ligands. Luminescence measurements were conducted and no uranyl emission was observed in either compound.

7.
Inorg Chem ; 56(15): 9156-9168, 2017 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-28742345

RESUMO

The syntheses and crystal structures of six new heterometallic compounds containing the UO22+ cation, o-, m-, and p-iodobenzoic acid ligands, and Tl+, Rb+, and Cs+ cations which adopt the role of both charge balancing cation and secondary metal center are described, as are the luminescent properties for Tl+ containing compounds 1, 4, and 6. The structures of compounds 1-3 are isomorphous and contain uranyl monomers bound by o-iodobenzoic acid ligands with Tl+, Rb+, and Cs+ cations acting as secondary metal centers. Compounds 4 and 5 are also isomorphous and feature m-iodobenzoic acid ligands bound to the uranyl cation along with Tl+ and Rb+ cations. Compound 6 is unique in this series as it is assembled from a dimeric uranyl unit and features p-iodobenzoic acid ligands and Tl+ cations which function as charge balancing secondary metal centers. Single crystal X-ray diffraction analysis of these materials suggests that the secondary metal cations are incorporated based on the size of their ionic radius (Tl+ < Rb+ < Cs+), which is directly related to the size of the "pocket" observed in 1-6. Further, Voronoi-Dirichlet tessellation and Hirshfeld surface analysis were used to probe the coordination environment of the secondary metal centers as part of ongoing efforts to develop metrics for determining the coordination number of secondary metal cations in similar systems.

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