Determination of actinide speciation in solution using high-energy X-ray scattering

High-energy X-ray scattering (HEXS) has been used to understand the coordination environment of the uranyl ion in a perchlorate solution. Assuming the two coordinating oxo ligands bound to U(VI) are represented in a peak in the pair distribution function (PDF) at 1.766(1) A, integration of the peak intensity is used to quantify the charge located on the oxygens. The dioxo ligands are essentially neutral, as predicted by numerous published calculations, with a charge of -16.4(8) electrons. The peak in the PDF at 2.420(1) A is consistent with equatorial ligating waters. The intensity of this peak is inconsistent with an integral coordination number and is used to propose a solution equilibrium of five and four waters coordinating to the uranyl(VI) ion favoring the five-coordinate species. This equilibrium is then used to experimentally determine that five-coordinate uranyl is 1.19+/-0.42 kcal/mol more stable than its four-coordinate counterpart under the conditions of the experiment. Further peaks in the Fourier transform of the scattering data at 4.50, 7, and 8.7 A are attributed to uranium-solvent correlations.     

Uranyl coordination environment in hydrophobic ionic liquids: an in situ investigation

Different inner-sphere coordination environments are observed for the uranyl nitrate complexes formed with octyl-phenyl-N,N-diisobutylcarbamoylmethylphosphine oxide and tributyl phosphate in dodecane and in the hydrophobic ionic liquids (ILs) [C(4)mim][PF(6)] and [C(8)mim][N(SO(2)CF(3))(2)]. Qualitative differences in the coordination environment of the extracted uranyl species are implied by changes in peak intensity patterns and locations for uranyl UV-visible spectral bands when the solvent is changed. EXAFS data for uranyl complexes in dodecane solutions is consistent with hexagonal bipyramidal coordination and the existence of UO(2)(NO(3))(2)(CMPO)(2). In contrast, the complexes formed when uranyl is transferred from aqueous nitric acid solutions into the ILs exhibit an average equatorial coordination number of approximately 4.5. Liquid/liquid extraction results for uranyl in both ILs indicate a net stoichiometry of UO(2)(NO(3))(CMPO)(+). The concentration of the IL cation in the aqueous phase increases in proportion to the amount of UO(2)(NO(3))(CMPO)(+) in the IL phase, supporting a predominantly cation exchange mechanism for partitioning in the IL systems.     

堆积模型在萃取中的应用I: 水相介质协同效应

根据推积模型提出一种新的协萃体系,即:(简单阴离子)1+(简单阴离子)2+萃取剂,并以实验证实了水相混合介质的协同效应.研究了UO2/OAc,C1/TBP-二甲苯体系的协萃效应,测定了萃合物的组成以及各种影响分配比的因素.     

Crystallographic controls on uranyl binding at the quartz/water interface

Molecular dynamics methods were used to simulate UO(2)(OH)(2)(0) binding to pairs of oxo sites (O(S)) on three low-index planes of α-SiO(2) in contact with water. Differences in binding site distributions on the (001), (010) and (101) planes produced distinct sets of stable U inner-sphere species. Steric constraints prevented bidentate coordination to the (001) surface, resulting in a mononuclear monodentate complex, [UO(2)(OH)(2)(H(2)O)(n)O(S)] (90% for n=1 and 10% for n=2 over 5 ns production runs). Binuclear bidentate coordination, [UO(2)(OH)(2)(H(2)O)(n)(O(S))(2)], was however favored on the (010) (99% for n=0 and 1% for n=1) and the (101) (72% for n=0 and 28% for n=1) planes. These results underscore a predominant four-coordinated equatorial shell for U when complexed to the quartz/water interface. Potential of mean force calculations uncovered a diversity of metastable outer- and inner-sphere complexes at local energy minima up to ～0.4 nm from the surface. These calculations point to important differences in both energetic requirements and mechanisms for the approach of UO(2)(OH)(2)(0) to different quartz surfaces. Binding strengths are affected by binding site distribution, steric freedom, U hydration and OH orientation, and increase in the order (001) (3.7 kJ mol(-1)) < (101) (5.6 kJ mol(-1)) < (010) (6.5 kJ mol(-1)). A general binding mechanism involves (1) formation of monodentate outer-sphere complexes, (2) removal of oxo-bound waters, (3) formation of one (monodentate), then two (bidentate) direct U-O(S) bonds (inner-sphere), and (4) expulsion of excessive waters from the equatorial shell of U.     

一系列水合和非水合铀酰卤族(F,Cl,Br)配合物在水溶液中的结构和紫外吸收光谱性质的密度泛函理论研究

本文考虑相对论效应并应用密度泛函理论(DFT)研究水溶液中UO2Xn(H2O)5-n(X=F,Cl,Br;n=1～4)和UO2Xn(X=F,Cl,Br;n=1～6)一系列水合和非水合铀酰化合物的结构和紫外吸收光谱性质。将这一系列物质命名为Xnm(X为F,Cl,和Br;n为卤素配体个数,m为水分子配体的个数)。在水溶液中,溶剂化效应采用类导体屏蔽模型(COSMO)并采用SAS溶剂接触曲面构造空穴模拟水溶剂对配合物的作用。配合物的紫外光谱性质采用考虑旋-轨耦合相对论效应的含时密度泛函(SO-TD-DFT)进行计算。U=O键随着F配体数目的增加而明显伸长,然而随Cl和Br配体数目的增加变化较小。随X配体数目的增加和水分子参与配位,铀与X的结合能逐渐减弱。配合物的紫外光谱计算表明铀酰氟的各种配合物并不出现特征吸收峰,而铀酰氯和铀酰溴的各种配合物均有特征吸收光谱。通过分子轨道分析可以很好解释光谱所体现的特征。     

Investigation of uranyl nitrate ion pairs complexed with amide ligands using electrospray ionization ion trap mass spectrometry and density functional theory

Ion populations formed from electrospray of uranyl nitrate solutions containing different amides vary depending on ligand nucleophilicity and steric crowding at the metal center. The most abundant species were ion pair complexes having the general formula [UO(2)(NO(3))(amide)(n=2,3)](+); however, singly charged complexes containing the amide conjugate base and reduced uranyl UO(2)(+) were also formed as were several doubly charged species. The formamide experiment produced the greatest diversity of species resulting from weaker amide binding, leading to dissociation and subsequent solvent coordination or metal reduction. Experiments using methyl formamide, dimethyl formamide, acetamide, and methyl acetamide produced ion pair and doubly charged complexes that were more abundant and less abundant complexes containing solvent or reduced uranyl. This pattern is reversed in the dimethylacetamide experiment, which displayed lower abundance doubly charged complexes, but augmented reduced uranyl complexes. DFT investigations of the tris-amide ion pair complexes showed that interligand repulsion distorts the amide ligands out of the uranyl equatorial plane and that complex stabilities do not increase with increasing amide nucleophilicity. Elimination of an amide ligand largely relieves the interligand repulsion, and the remaining amide ligands become closely aligned with the equatorial plane in the structures of the bis-amide ligands. The studies show that the phenomenological distribution of coordination complexes in a metal-ligand electrospray experiment is a function of both ligand nucleophilicity and interligand repulsion and that the latter factor begins exerting influence even in the case of relatively small ligands like the substituted methyl-formamide and methyl-acetamide ligands.     

Uranyl-peptide interactions in carbonate solution with DAHK and derivatives

Metal-peptide complexes in a 1:1 ratio between the uranyl cation (UO2(2+)) and the peptides, DAHK or GGH, are observed in the gas phase (ESI-MS). Solution state studies with the same peptides and variants, DGHG, AcDGHG, and DAHKSE-CONH2, indicate that peptide-carboxylato donors can coordinate to the uranyl biscarbonato complex. UV-vis and fluorescence spectra of uranyl carbonate exhibit significant changes or quenching upon addition of peptide. NMR titration data were used to determine conditional association constants, log K = 2.2+/-0.4 and log K = 3.1+/-0.4, for the [UO2(CO3)2(GGH)] and [UO2(CO3)2(DAHK)] species, respectively. Uranyl asymmetric stretching frequencies for uranyl/ DAHKSE-CONH2 (v3 = 914 cm(-1)) and uranyl/DAHK (v3 = 908 cm(-1)) complexes and other infrared spectral features are also consistent with peptide-carboxylato coordination.     

Structure of [UO2Cl4]2- in acetonitrile

The complex formation of uranyl UO(2)(2+) with chloride ions in acetonitrile was studied by UV-vis and U L(III) EXAFS spectroscopy. The investigations unambiguously point to the existence of a [UO(2)Cl(4)](2-) species in solution with D(4)(h)() symmetry. The distances in the U(VI) coordination sphere are U-O(ax) = 1.77 +/- 0.01 Angstroms and U-Cl = 2.68 +/- 0.01 Angstroms.     

A trigonal bipyramidal uranyl amido complex: synthesis and structural characterization of [Na(THF)2][UO2(N(SiMe3)2)3

The synthesis and structural characterization of a rare example of a uranyl complex possessing three equatorial ligands, [M(THF)2][UO2(N(SiMe3)2)3] (3a, M = Na; 3b, M = K), are described. The sodium salt 3a is prepared by protonolysis of [Na(THF)2]2[UO2(N(SiMe3)2)4], whereas the potassium salt 3b is obtained via a metathesis reaction of uranyl chloride UO2Cl2(THF)2 (4) with 3 equiv of K[N(SiMe3)2]. A single-crystal X-ray diffraction study of 3a revealed a trigonal-bipyramidal geometry about uranium, formed by two axial oxo and three equatorial amido ligands, with average U=O and U-N bond distances of 1.796(5) and 2.310(4) A, respectively. One of the oxo ligands is also coordinated to the sodium counterion. 1H NMR spectroscopic studies indicate that THF adds reversibly as a ligand to 3 to expand the trigonal bipyramidal geometry. The degree to which the coordination sphere in 3 is electronically satisfied with only three amido donors is suggested by (1) the reversible THF coordination, (2) a modest elongation in the bond distances for a five-coordinate U(VI) complex, and (3) the basicity of the oxo ligands as evidenced in the contact to Na. The vibrational spectra of the series of uranyl amido complexes [UO2(N(SiMe3)2)n]2-n (n = 2-4) are compared, to evaluate the effects on the axial U=O bonding as a function of increased electron density donated from the equatorial region. Raman spectroscopic measurements of the nu 1 symmetric O=U=O stretch show progressive axial bond weakening as the number of amido donors is increased. Crystal data for [Na(THF)2][UO2(N(SiMe3)2)3]: orthorhombic space group Pna2(1), a = 22.945(1) A, b = 15.2830(7) A, c = 12.6787(6) A, z = 4, R1 = 0.0309, wR2 = 0.0524.     

Theoretical investigations of uranyl-ligand bonding: four- and five-coordinate uranyl cyanide, isocyanide, carbonyl, and hydroxide complexes

The coordination and bonding of equatorial hydroxide, carbonyl, cyanide (CN-), and isocyanide (NC-) ligands with uranyl dication, [UO2]2+, has been studied using density functional theory with relativistic effective core potentials. Good agreement is seen between experimental and calculated geometries of [UO2(OH)4]2-. Newly predicted ground-state structures of [UO2(OH)5]3-, [UO2(CO)4]2+, [UO2(CO)5]2+, [UO2(CN)4]2-, [UO2(CN)5]3-, [UO2(NC)4]2-, and [UO2(NC)5]3- are reported. Four-coordinate uranyl isocyanide complexes are the predicted gas-phase species while five-coordinate uranyl cyanide complexes are energetically favorable in aqueous solution. Small energy differences between cyanide and isocyanide complexes indicate the energetic feasibility of mixed cyanide and isocyanide complexes. A D2d uranyl tetrahydroxide is the dominant gas-phase and aqueous species, but formation of uranyl carbonyl complexes is seen to be exothermic in the gas-phase and endothermic in aqueous solution.     

Coordination properties of ionic liquid-mediated chromium(II) and copper(II) chlorides and their complexes with glucose

The structural and coordination properties of complexes formed upon the interaction of copper(II) and chromium(II) chlorides with dialkylimidazolium chloride (RMIm(+)Cl(-)) ionic liquids and glucose are studied by a combination of density functional theory (DFT) calculations and X-ray absorption spectroscopy (XAS). In the absence of the carbohydrate substrate, isolated mononuclear four-coordinated MeCl(4)(2-) species (Me = Cu, Cr) dominate in the ionic liquid solution. The organic part of the ionic liquid does not directly interact with the metal centers. The interactions between the RMIm(+) cations and the anionic metal chloride complexes are limited to hydrogen bonding with the basic Cl(-) ligands and the overall electrostatic stabilization of the anionic metal complexes. Exchange of Cl(-) ligands by a hydroxyl group of glucose is only favorable for CrCl(4)(2-). For Cu(2+) complexes, the formation of hydrogen bonded complexes between CuCl(4)(2-) and glucose is preferred. No preference for the coordination of metal chloride species to specific hydroxyl group of the carbohydrate is found. The formation of binuclear metal chloride complexes is also considered. The reactivity and selectivity patterns of the Lewis acid catalyzed reactions of glucose are discussed in the framework of the obtained results.     

Redox energetics and kinetics of uranyl coordination complexes in aqueous solution

Detailed voltammetric results for five uranyl coordination complexes are presented and analyzed using digital simulations of the voltammetric data to extract thermodynamic (E(1/2)) and heterogeneous electron-transfer kinetic (k(0) and alpha) parameters for the one-electron reduction of UO(2)(2+) to UO(2)(+). The complexes and their corresponding electrochemical parameters are the following: [UO(2)(OH(2))(5)](2+) (E(1/2) = -0.169 V vs Ag/AgCl, k(0) = 9.0 x 10(-3) cm/s, and alpha = 0.50); [UO(2)(OH)(5)](3-) (-0.927 V, 2.8 x 10(-3) cm/s, 0.46); [UO(2)(C(2)H(3)O(2))(3)](-) (-0.396 V, approximately 0.1 cm/s, approximately 0.5); [UO(2)(CO(3))(3)](4-) (-0.820 V, 2.6 x 10(-5) cm/s, 0.41); [UO(2)Cl(4)](2-) (-0.065 V, 9.2 x 10(-3) cm/s, 0.30). Differences in the E(1/2) values are attributable principally to differences in the basicity of the equatorial ligands. Differences in rate constants are considered within the context of Marcus theory of electron transfer, but no specific structural change(s) in the complexes between the two oxidation states can be uniquely identified with the underlying variability in the heterogeneous rate constants and electron-transfer coefficients.     

Electronic spectra of uranyl chloride complexes in acetone: a CASSCF/CASPT2 investigation

A theoretical study is presented of the electronic spectra of the complexes UO(2)Cl(2)ac(4), UO(2)Cl(2)ac(3), [UO(2)Cl(3)ac(2)](-) and [UO(2)Cl(3)ac](-) (ac = acetone) using perturbation theory based on a complete-active-space type wavefunction (CASSCF/CASPT2). Both scalar relativistic effects and spin-orbit coupling were included in the calculations. The calculated excitation energies and oscillator strength values have been compared to the experimental absorption spectrum for uranyl chloride complexes in acetone solution, for chloride-to-uranyl ratios between two and three. The main purpose of this work was to investigate the origin of the remarkable intensity increase observed in the lower part of the experimental absorption spectra, upon addition of chloride to uranyl complexes in acetone. The calculated excitation energies for the different complexes are similar and closely correspond to the experimental data. However, in none of the theoretical spectra, the high intensities observed in the lower part of the experimental spectrum are reproduced.     

Anhydrous photochemical uranyl(VI) reduction: unprecedented retention of equatorial coordination accompanying reversible axial oxo/alkoxide exchange

In a dramatic reversal of the normal trend of observed reactivity in uranyl(VI) coordination chemistry, an unprecedented retention of the normally labile equatorial coordination plane accompanies facile and reversible axial oxo/alkoxide exchange during both the photochemical reduction of cationic uranyl(VI) phosphine-oxide complexes with organic substrates and subsequent hydrolysis of the uranium(IV) alkoxide complexes to regenerate the uranyl(VI) starting complex.     

Structural units in three uranyl perrhenates

Three uranyl perrhenates have been synthesized, and their structures have been determined. (UO2)2(ReO4)4(H2O)3 (1) is triclinic, space group P, a=5.2771(7), b=13.100(2), c=15.476(2) A, alpha=107.180(2), beta=99.131(3), gamma=94.114(2) degrees, V=1001.12 A3, Z=2. [(UO2)4(ReO4)2O(OH)4(H2O)7](H2O)5 (2) is also triclinic, space group P, a=7.884(1), b=11.443(2), c=16.976(2) A, alpha=83.195(4), beta=89.387(4), gamma=85.289(4) degrees, V=1515.70 A3, Z=2. Na(UO2)(ReO4)3(H2O)2 (3) is monoclinic, space group C2/m, a=12.311(3), b=22.651(6), c=5.490(1) A, beta=109.366(6) degrees, V=1444.24 A3, Z=4. These compounds are the first structurally characterized uranyl perrhenates that do not contain organic ligands. In each structure, perrhenate groups coordinate uranyl ions at the equatorial vertices of pentagonal bipyramids. 1 contains complex chains of uranyl pentagonal bipyramids that are bridged by vertex sharing with perrhenate groups. The structural units in 2 and 3 consist of three novel finite clusters that include the coordination of uranyl ions with perrhenate. In general, weakly coordinating ligands such as perchlorate, perrhenate, and pertechnetate are assumed not to form stable complexes with uranyl in solutions or solids. The current findings, together with other recently reported studies, indicate each of these ligands can coordinate uranyl, and novel structure types result.     

Spectroscopic evidence for the direct coordination of the pertechnetate anion to the uranyl cation in [UO2(TcO4)(DPPMO2)2]+

We report the synthesis and structural characterization of [UO(2)(ReO(4))(DPPMO(2))(2)][ReO(4)] and [UO(2)(Cl)(DPPMO(2))(2)][Cl] (where DPPMO(2) = bis(diphenylphosphino)methane dioxide). In both complexes, the linear uranyl dication is coordinated to two bidentate DPPMO(2) ligands in the equatorial plane with one coordinated and one non-coordinated anion (either perrhenate or chloride). We have also prepared the pertechnetate analogue, and, through (31)P and (99)Tc NMR, we have shown that the cation, [UO(2)(TcO(4))(DPPMO(2))(2)](+), is stable in solution.     

Experimental and theoretical studies on ferromagnetically coupled metal complexes with imino nitroxides

Copper(II), zinc(II), and nickel(II) complexes with tridentate imino nitroxyl diradicals, [CuCl(bisimpy)(MeOH)](PF(6)) (1), [ZnCl(2)(bisimpy)] (2), and [NiCl(bisimpy)(H(2)O)(2)]Cl x 2H(2)O (3) (bisimpy = 2,6-bis(1'-oxyl-4',4',5',5'-tetramethyl-4',5'-dihydro-1'H-imidazol-2'-yl)pyridine), were prepared, and their magnetic properties were studied. In 1, the Cu(II) ion has a square pyramidal coordination geometry, of which the equatorial coordination sites are occupied by three nitrogen atoms from the bisimpy and a chloride ion. The coordination geometry of the Zn(II) ion in 2 can be described as a trigonal bipyramid, with two chloride ions and a bisimpy. In 3, the Ni(II) ion has a distorted octahedral coordination geometry, of which four coordination sites are coordinated by the bisimpy and chloride ion, and two water molecules occupy the remaining cis positions. Magnetic susceptibility and EPR measurements revealed that in 1 and 3 the Cu(II) and Ni(II) ions with imino nitroxyl diradicals were ferromagnetically coupled, with the coupling constants J (H = -2J(ij) summation operator S(i)S(j)) of +165(1) and 109(2) cm(-1), respectively, and the intraligand ferromagnetic interactions in 1-3 were very weak. DFT molecular orbital calculations were performed on the diradical ligand, 1, and 2 to study the spin density distribution before and after coordination to the metal ions.     

Complex Formation in the Ternary System Tl(III)-CN(-)-Cl(-) in Aqueous Solution. A (205)Tl NMR Study

The existence of mixed complexes of the general formula Tl(CN)(m)()Cl(n)()(3)(-)(m)()(-)(n)() (m + n 相似文献   

Role of the uranyl oxo group as a hydrogen bond acceptor

Density functional theory calculations have been used to evaluate the geometries and energetics of interactions between a number of uranyl complexes and hydrogen bond donor groups. The results reveal that although traditional hydrogen bond donors are repelled by the oxo group in the [UO(2)(OH(2))(5)](2+) species, they are attracted to the oxo groups in [UO(2)(OH(2))(2)(NO(3))(2)](0), [UO(2)(NO(3))(3)](-), and [UO(2)Cl(4)](2-) species. Hydrogen bond strength depends on the equatorial ligation and can exceed 15 kcal mol(-1). The results also reveal the existence of directionality at the uranyl oxo acceptor, with a weak preference for linear U═O---H angles.     

尾式金属卟啉配合物的研究IV: 含氮配体与尾式铁(III)卟啉轴向配位反应热力学及其配位模式

用分光光度法研究了咪唑或吡啶类配体与5-[邻-(4-(1-咪唑基)丁氧基)苯基]-10,15,20-三苯基卟啉合铁(III)氯化物[[Fe^I^I^I(ImTPP)]Cl]和5-[对-(4-(3-吡啶氧基)丁氧基)苯基]10,15,20-三苯基卟啉合铁(III)氯化物[[Fe^I^I^I(PyTPP)]Cl]两种尾式铁(III)卟啉的轴向加合作用, 测定了平衡常数、热力学参数及含氮配体的加合分子数。结果表明, [Fe^I^I^I(PyTPP)Cl与[Fe^I^I^I(TPP)]Cl相类似, 均与咪唑、吡啶类配体生成1:2低自旋六配位加合物。含氮配体与[Fe^I^I^I(ImTPP)]Cl的轴向加合反应平衡常数比与{Fe^I^I^I(TPP)]Cl相应的平衡常数大10-10^3倍, 这是因为含氮配体与[Fe^I^I^I(ImTPP)]Cl的轴向配位诱导了尾端咪唑基与配合物中的Fe^I^I^I离子的轴向配位, 这种配位横式增强了含氮配体与Fe^I^I^I离子的键合; 尾端咪唑基与配合物中的Fe^I^I^I离子配位的模式得到了UV-vis、^1H NMR及EPR实验数据的进一步证实。