Solvation of uranyl(II), europium(III) and europium(II) cations in "basic" room-temperature ionic liquids: a theoretical study

We report a molecular dynamics study of the solvation of UO2(2+), Eu3+ and Eu2+ ions in two "basic" (Lewis acidity) room-temperature ionic liquids (IL) composed of the 1-ethyl-3-methylimidazolium cation (EMI+) and a mixture of AlCl4- and Cl- anions, in which the Cl-/AlCl4- ratio is about 1 and 3, respectively. The study reveals the importance of the [UO2Cl4]2- species, which spontaneously form during most simulations, and that the first solvation shell of europium is filled with Cl- and AlCl4- ions embedded in a cationic EMI+ shell. The stability of the [UO2Cl4]2- and [Eu(III)Cl6]3- complexes is supported by quantum mechanical calculations, according to which the uranyl and europium cations intrinsically prefer Cl- to the AlCl4- ion. In the gas phase, however, [Eu(III)Cl6]3- and [Eu(II)Cl6]4- complexes are predicted to be metastable and to lose two to three Cl- ions. This contrasts with the results of simulations of complexes in ILs, in which the "solvation" of the europium complexes increases with the number of coordinated chlorides, leading to an equilibrium between different chloro species. The behavior of the hydrated [Eu(OH2)8]3+ complex is considered in the basic liquids; the complex exchanges H2O molecules with Cl- ions to form mixed [EuCl3(OH2)4] and [EuCl4(OH2)3]- complexes. The results of the simulations allow us to better understand the microscopic nature and solvation of lanthanide and actinide complexes in "basic" ionic liquids.     

Identical extraction behavior and coordination of trivalent or hexavalent f-element cations using ionic liquid and molecular solvents

The extraction of both UO2(2+) and trivalent lanthanide and actinide ions (Am3+, Nd3+, Eu3+) by dialkylphosphoric or dialkylphosphinic acids from aqueous solutions into the ionic liquid, 1-decyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide has been studied and compared to extractions into dodecane. Radiotracer partitioning measurements show comparable patterns of distribution ratios for both the ionic liquid/aqueous and dodecane/aqueous systems, and the limiting slopes at low acidity indicate the partitioning of neutral complexes in both solvent systems. The metal ion coordination environment, elucidated from EXAFS and UV-visible spectroscopy measurements, is equivalent in the ionic liquid and dodecane solutions with coordination of the uranyl cation by two hydrogen-bonded extractant dimers, and of the trivalent cations by three extractant dimers. This is the first definitive report of a system where both the biphasic extraction equilibria and metal coordination environment are the same in an ionic liquid and a molecular organic solvent.     

Complexation of lanthanides, actinides and transition metal cations with a 6-(1,2,4-triazin-3-yl)-2,2':6',2'-terpyridine ligand: implications for actinide(III)/lanthanide(III) partitioning

The quadridentate N-heterocyclic ligand 6-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2'?:?6',2'-terpyridine (CyMe(4)-hemi-BTBP) has been synthesized and its interactions with Am(III), U(VI), Ln(III) and some transition metal cations have been evaluated by X-ray crystallographic analysis, Am(III)/Eu(III) solvent extraction experiments, UV absorption spectrophotometry, NMR studies and ESI-MS. Structures of 1:1 complexes with Eu(III), Ce(III) and the linear uranyl (UO(2)(2+)) ion were obtained by X-ray crystallographic analysis, and they showed similar coordination behavior to related BTBP complexes. In methanol, the stability constants of the Ln(III) complexes are slightly lower than those of the analogous quadridentate bis-triazine BTBP ligands, while the stability constant for the Yb(III) complex is higher. (1)H NMR titrations and ESI-MS with lanthanide nitrates showed that the ligand forms only 1:1 complexes with Eu(III), Ce(III) and Yb(III), while both 1:1 and 1:2 complexes were formed with La(III) and Y(III) in acetonitrile. A mixture of isomeric chiral 2:2 helical complexes was formed with Cu(I), with a slight preference (1.4:1) for a single directional isomer. In contrast, a 1:1 complex was observed with the larger Ag(I) ion. The ligand was unable to extract Am(III) or Eu(III) from nitric acid solutions into 1-octanol, except in the presence of a synergist at low acidity. The results show that the presence of two outer 1,2,4-triazine rings is required for the efficient extraction and separation of An(III) from Ln(III) by quadridentate N-donor ligands.     

Differences of Eu(III) and Cm(III) chemistry in ionic liquids: investigations by TRLFS

In this study the coordination structure and chemistry of Eu(III) and Cm(III) in the ionic liquid C(4)mimTf(2)N (1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) was investigated by time-resolved laser fluorescence spectroscopy (TRLFS). The dissolution of 1 x 10(-2) M Eu(CF(3)SO(3))(3) and 1 x 10(-7) M Cm(ClO(4))(3) in C(4)mimTf(2)N leads to the formation of two species for each cation with fluorescence emission lifetimes of 2.5 +/- 0.2 ms and 1.0 +/- 0.3 ms for the Eu-species and 1.0 +/- 0.3 ms and 300.0 +/- 50 micros for the Cm-species. The interpretation of the TRLFS data indicates a comparable coordination for both the lanthanide and actinide cation in this ionic liquid. The quenching influence of Cu(II) on the fluorescence emission of Eu(III) and Cm(III) was also measured by TRLFS. While Cu(ii) does not quench the Cm(III) fluorescence emission in C(4)mimTf(2)N the Eu(III) fluorescence emission lifetime for both Eu-species in C(4)mimTf(2)N decreases with increasing Cu(II) concentration. Stern-Volmer constants were calculated (k(SV) = 1.54 x 10(6) M(-1) s(-1) and k(SV) = 2.70 x 10(6) M(-1)). By contrast, the interaction of Cu(II) with Eu(III) and Cm(III) in water leads to a quenching of both the lanthanide and actinide fluorescence. The calculated Stern-Volmer constants are 1.20 x 10(4) M(-1) s(-1) for Eu(III) and 1.27 x 10(4) M(-1) s(-1) for Cm(III). The investigations show, while the chemistry of trivalent lanthanides and actinides is similar in an aqueous system it is dramatically different in ionic liquids. This difference in chemical behavior may provide the opportunity for a separation of lanthanides and actinides with regard to the reprocessing of nuclear fuel.     

Theoretical studies on the complexation of Eu(III) and Am(III) with HDEHP: structure,bonding nature and stability

Separation of trivalent lanthanides (Ln(III)) and actinides (An(III)) is a key issue in the advanced spent nuclear fuel reprocessing. In the well-known trivalent actinide lanthanide separation by phosphorus reagent extraction from aqueous komplexes (TALSPEAK) process, the organophosphorus ligand HDEHP (di-(2-ethylhexyl) phosphoric acid) has been used as an efficient reagent for the partitioning of Ln(III) from An(III) with the combination of a holdback reagent in aqueous lactate buffer solution. In this work, the structural and electronic properties of Eu³⁺ and Am³⁺ complexes with HDEHP in nitric acid solution have been systematically explored by using scalar-relativistic density functional theory (DFT). It was found that HDEHP can coordinate with M(III) (M=Eu, Am) cations in the form of hydrogen-bonded dimers HL₂^- (L=DEHP), and the metal ions prefer to coordinate with the phosphoryl oxygen atom of the ligand. For all the extraction complexes, the metal-ligand bonds are mainly ionic in nature. Although Eu(III) complexes have higher interaction energies, the HL₂^- dimer shows comparable affinity for Eu(III) and Am(III) according to thermodynamic analysis, which may be attributed to the higher stabilities of Eu(III) nonahydrate. It is expected that this work could provide insightful information on the complexation of An(III) and Ln(III) with HDEHP at the molecular level.     

Trivalent actinide and lanthanide separations by tetradentate nitrogen ligands: a quantum chemistry study

Although a variety of tetradentate ligands, 6,6'-bis(5,6-dialkyl-1,2,4-triazin-3-yl)-2,2'-bipyridines (BTBPs), have been proved as effective ligands for selective extraction of Am(III) over Eu(III) experimentally, the origin of their selectivity is still an open question. To elucidate this question, the geometric and electronic structures of the actinide and lanthanide complexes with the BTBPs have been investigated systematically by using relativistic quantum chemistry calculations. We show herein that in 1:1 (metal:ligand) type complexes substitution of electron-donating groups to the BTBP molecule can enhance its coordination ability and thus the energetic stability of the formed Am(III) and Eu(III) complexes in the gas phase. According to our results, Eu(III) can coordinate to the BTBPs with higher stability in energy than Am(III), no matter whether there are nitrate ions in the inner-sphere complexes. The presence of nitrate ions leads to formation of the probable Am(III) and Eu(III) complexes, M(NO(3))(3)(H(2)O)(n) (M = Am, Eu), in nitric acid solutions. It has been found that the changes of Gibbs free energy play an important role for Am(III)/Eu(III) separation. In fact, the weaker complexing ability of Am(III) with nitrate ions and water molecules makes the decomposition of Am(NO(3))(3)(H(2)O)(4) more favorable in energy, which may thus increase the possibility of formation of Am(BTBPs)(NO(3))(3). Our work may shed light on the design of novel extractants for Am(III)/Eu(III) separation.     

EXAFS and time-resolved laser fluorescence spectroscopy (TRLFS) investigations of the structure of Cm(III)/Eu(III) complexed with di(chlorophenyl)dithiophosphinic acid and different synergistic agents

The complexes of trivalent actinide curium (Cm(III)) with di(chlorophenyl)dithiophosphinic acid ((ClPh)2PSSH) and three different neutral complexing agents as synergists in tert-butylbenzene are studied by EXAFS and time-resolved laser fluorescence spectroscopy (TRLFS). The results are compared with those from the corresponding europium (Eu(III)) complexes. The aim of these investigations is to understand the chemical interactions responsible for the high selectivity of the synergistic systems of (ClPh)2PSSH and neutral complexing agents tri-n-octylphosphine oxide, tributylphosphate and tris(2-ethylhexyl)phosphate for trivalent actinide cations in liquid-liquid extraction. In our structural chemistry study, we find that the inner coordination sphere of extracted Cm(III) and Eu(III) complexes are different. In all complexes the (ClPh)2PSSH is bound to the metal cation in a bidentate fashion and the oxygen donor of the neutral complexing agent used as synergist is directly coordinated to the metal cation. Comparison of the Cm(III) and Eu(III) complexes shows that Cm(III) preferentially binds to the sulfur of (ClPh)2PSSH, whereas Eu(III) is preferentially bound to oxygen. A good selectivity in liquid-liquid extraction is correlated with a high ratio of the sulfur coordination number to oxygen coordination number. This leads to the conclusion that the observed differences in the coordination structure between Cm(III) and Eu(III) complexes play an important role in the selectivity of these extraction systems.     

Time-resolved laser fluorescence spectroscopy and extended X-ray absorption spectroscopy investigations of the N3- complexation of Eu(III), Cm(III), and Am(III) in an ionic liquid: differences and similarities

The complexation of the lanthanide Eu(III) and the actinides Cm(III) and Am(III) by N3- was investigated by application of time-resolved laser fluorescence spectroscopy (TRLFS) and X-ray absorption spectroscopy (XAFS) in the ionic liquid solution of C4mimTf2N (1-butyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide). TRLFS measurements show that the interaction of azide with Eu(CF3SO3)3 and Eu(ClO4)3 results in both dynamic luminescence quenching by collisional encounters of N3- with Eu(III) and static luminescence quenching by inner-sphere complexation of Eu(III) by N3-. Hereby, the complexation of Eu-triflate by azide starts at a lower N3- concentration as compared to the perchlorate salt. The authors ascribe this phenomenon to a stronger bonding of ClO4- toward the metal ion than triflate, as well as to a stronger electrostatic repulsion of N3- by the perchlorate ligand. In both actinide samples (Cm(ClO4)3, Am(ClO4)3), the complexation with azide exhibits a clear kinetic hindrance. Nevertheless, mixed actinide-perchlorate-azide complexes are formed after several days in C4mimTf2N. The different reaction kinetics for the Ln- and An-complexation by azide may provide the opportunity for an effective separation of lanthanides from actinides in the nuclear fuel cycle by the use of N-based extractants in ionic liquid solution.     

Extraction of actinides by dibutyl-N,N-diethylcarbamoylmethylenephosphonate [DBDECMP] from nitric acid solutions

The extraction of Am(III), Pu(IV) and U(VI) as representatives of tri-, tetra- and hexavalent actinides by dibutyl-N,N-diethylcarbamoylmethylenephosphonate (DBDECMP) from nitric acid solution has ben studied with an objective of understanding the extraction mechanism. The dependence of the distribution ratios of the actinide ions was studied as a function of the concentration of H⁺, DBDECMP and NO ₃ ^– . The extraction data revealed that all the three actinide ions are extracted as their neutral nitrate complexes solvated by DBDECMP which behaves as neutral extractant only. The absorption spectra of DBDECMP and TBP extracts of these actinide ions were recorded. From the close similarity of these spectra it is inferred that DBDECMP acts as a monodentate extractant in the present system.     

Thermodynamics of thiocyanate complexes of trivalent actinides and lanthanides

The thermodynamic parameters ΔF, ΔH and ΔS of the complexes of Cm(III), C(III) and Tm(III) with the SCN^? ion have been determined at 30°C in ammonium ion medium of unit ionic strength by the temperature variation method. It has been concluded that both the thiocyanate complexes of trivalent actinides and lanthanides are predominantly inner-sphere type. The higher stability of the second complexes of trivalent actinides is reflected either in the enthalpy or the entropy change depending on the degree of hydration of the trivalent actinide ions. The implications of the greater free energy change for PuSCN²⁺ as compared with other trivalent actinide or lanthanide first thiocyanate complexes are discussed.     

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.     

Crown ether inclusion complexes of the early actinide elements, [AnO2(18-crown-6)]n+, An = U, Np, Pu and n = 1, 2: a relativistic density functional study

The title compounds, [AnO2(18-crown-6)]n+, An = U, Np, and Pu and n = 1 and 2, as well as the related (experimentally observed) complex [UO2(dicyclohexyl-18-crown-6)]2+ are studied using relativistic density functional theory (DFT). Different relativistic methods (large-core and small-core effective core potentials, all-electron scalar four-component) and two flavors of approximate DFT (B3LYP and PBE) are used. Calculated bond lengths agree well with the available experimental data for the NpV complex, while larger differences for the UVI complexes appear to be related to the large uncertainties in the experimental data. The axial AnO bonds are found to be weaker and longer than in the corresponding penta-aquo complexes, though still of partial triple-bond character. The AnO bond lengths and strengths decrease along the actinide series, consistent with the actinide contraction. Gas-phase binding energies calculated for the penta-aquo complexes and crown-ether complexes of the actinides studied, as well as ligand-exchange energies, show that there is no intrinsic preference, or "better fit", for actinyl(V) cations as compared to actinyl(VI) ones. Rather, the ability of NpO2+ (NpV) to form in-cavity 18-crown-6 complexes in water, which is impossible for UO22+, is traced to solvation effects in polar solvents. Thus, the experimentally observed stabilization of the pentavalent oxidation state as compared to the hexavalent one is due to the effective screening of the charge provided by the macrocycle, and this leads to destabilization of the AnVI crown complexes relative to their AnV counterparts.     

Novel phosphorylated calixarenes for the recognition of f-elements

The binding properties of three series of phosphorylated calixarene derivatives bearing phosphine oxide or phosphonate groups either at the wide or the narrow rims have been investigated towards some representative lanthanide and actinide ions using several approaches: (i) liquid–liquid extraction of europium, americium, thorium and uranyl ions from nitric acid solutions into the two diluents m-nitrobenzotrifluoride (m-NBTF) or dichloromethane; (ii) complexation in single media (methanol and acetonitrile) followed by UV-spectrophotometric and isoperibolic (micro)calorimetric titrations (ITC). The latter technique was found to be very useful for the determination of the stoichiometries of the complexes formed, in particular when the complexation did not induce significant spectral changes. It also provided a full thermodynamic characterization of these new systems. The influence of some structural features of the ligands as the nature of the substituents and the condensation degree of the calixarene moiety, on the distribution coefficients and on the complexation thermodynamic parameters has been established.     

Modeling adsorption of the uranyl dication on the hydroxylated alpha-Al2O3(0001) surface in an aqueous medium. Density functional study

As a first step toward modeling the interaction of dissolved actinide contaminants with mineral surfaces, we studied low-coverage adsorption of aqueous uranyl, UO2(2+), on the hydroxylated alpha-Al2O3(0001) surface. We carried out density functional periodic slab model calculations and modeled solvation effects by explicit aqua ligands. We explored the formation of both inner- and outer-sphere complexes and estimated the corresponding adsorption energies. Effects of solvation were accounted for by explicit consideration of the first hydration shell of uranyl and by means of a posteriori corrections for long-range solvent effect. With energetics described at the GGA-PW91 level and under the assumption of a fully protonated ideal surface, we predict a weakly bound outer-sphere adsorption complex.     

Complexation and the laser luminescence studies of Eu(III), Am(III), and Cm(III) with EDTA,CDTA, and PDTA and their ternary complexation with dicarboxylates

Spectroscopy has been used to determine the number of coordinated water molecules bound to Eu(III) and Cm(III) in a series of binary complexes of polyaminocarboxylate and their ternary complexes with dicarboxylates as well as with similar ligands with additional O-, N-, and S-donors. Complexes of Eu(III) and Cm(III) with polyaminocarboxylate alone contain ca. 2.5–3.0 waters of hydration. Increasing the steric requirement of a polyaminocarboxylate by increasing the number of groups in the ligand backbone does not appreciably change the hydration of these cations. The stability constants of the binary and ternary complexes of Cm(III), Am(III), and Eu(III) with these ligands were measured by solvent extraction in a solution of 0.1 M (NaClO₄). The size, basicity, specific M³⁺-second ligand interactions, and steric requirement of the ligands are the factors which affect the ternary complexation. Knowledge of the chemical species formed by actinide cations with organic ligands (carboxylates and aminocarboxylates), which are present in all nuclear waste, is important to understand the behavior of waste forms and the migration behavior of actinides in the environment.     

Use of ion exchange for the determination of stability constants of metal-humic substance complexes

Humic substances (HSs) occur throughout the ecosphere in soils, waters and underground systems. The strong complexation of HSs is of importance in the migration of radionuclies in geological media. Renewed interest in stability constants of complexes of radioelements and radionuclides with humic and fulvic acids has been generated by problems associated with the nuclide migration in the environment. Use of the ion exchange method for the determination of conditional stability constants of metal-HS complexes was examined and reviewed. The complexation of HS to metal ions cannot be described in rigorous mathematical terms because of the ill-defined nature of HSs in contrast with the complexation of single ligands. Furthermore, the advantages and disadvantages of Schubert's and, Ardakani-Stevenson's, curve fitting methods were discussed. The great stabilities of HS complexes to rare earths (Yb(III), Tb(III), Eu(III), Gd(III)), americium(III), cobalt(II), uranyl(VI) and thorium(IV) were revealed.     

2,6-Bis(5-(2,2-dimethylpropyl)-1H-pyrazol-3-yl)pyridine as a ligand for efficient actinide(III)/lanthanide(III) separation

The N-donor complexing ligand 2,6-bis(5-(2,2-dimethylpropyl)-1H-pyrazol-3-yl)pyridine (C5-BPP) was synthesized and screened as an extracting agent selective for trivalent actinide cations over lanthanides. C5-BPP extracts Am(III) from up to 1 mol/L HNO(3) with a separation factor over Eu(III) of approximately 100. Due to its good performance as an extracting agent, the complexation of trivalent actinides and lanthanides with C5-BPP was studied. The solid-state compounds [Ln(C5-BPP)(NO(3))(3)(DMF)] (Ln = Sm(III), Eu(III)) were synthesized, fully characterized, and compared to the solution structure of the Am(III) 1:1 complex [Am(C5-BPP)(NO(3))(3)]. The high stability constant of log β(3) = 14.8 ± 0.4 determined for the Cm(III) 1:3 complex is in line with C5-BPP's high distribution ratios for Am(III) observed in extraction experiments.     

Combination of size selective binding ability of 18-crown-6 dissolved in aqueous phase and extractive properties of an amic acid; toward enhancement of rare earths separation

The separation of La(III), Eu(III) and Er(III) ions by an amic acid, N,N-dioctyldiglycolamic acid (HL), dissolved in carbon tetrachloride has been improved in the presence of 18-crown-6 (18C6) in aqueous phase as a selective masking agent. The interaction between the studied metal ions and 18C6 resulted a shift in the extraction curve of the studied metal ions versus pH toward higher pH region. The displacement of the extraction curves was more pronounced for lanthanum ions and was varied as La(III) > Eu(III) > Er(III). This order of complexing ability of 18C6 toward the studied ions was attributed to the size adaptation of the ions and that of the crown ether cavity. The stability constants of the lanthanide–crown ether complexes in aqueous phase were evaluated. The influence of temperature on the extraction of studied metal ions from aqueous phase in the absence and the presence of 18C6 was tested in the range 298–308 K. This investigation allowed evaluating the thermodynamic parameters associated with the extraction process and those of the complexation of cations by 18C6 in the aqueous phase.     

Elucidation of the collision induced dissociation pathways of water and alcohol coordinated complexes containing the uranyl cation

Multiple-stage tandem mass spectrometry was used to characterize the dissociation pathways for complexes composed of (1) the uranyl ion, (2) nitrate or hydroxide, and (3) water or alcohol. The complex ions were derived from electrospray ionization (ESI) of solutions of uranyl nitrate in H2O or mixtures of H2O and alcohol. In general, collisional induced dissociation (CID) of the uranyl complexes resulted in elimination of coordinating water and alcohol ligands. For undercoordinated complexes containing nitrate and one or two coordinating alcohol molecules, the elimination of nitric acid was observed, leaving an ion pair composed of the uranyl cation and an alkoxide. For complexes with coordinating water molecules, MS(n) led to the generation of either [UO2(2+)OH-] or [UO2(2+)NO3(-)]. Subsequent CID of [UO2(2+)OH-] produced UO2(+). The base peak in the spectrum generated by the dissociation of [UO2(2+)NO3(-)], however, was an H2O adduct to UO2(+). The abundance of the species was greater than expected based on previous experimental measurements of the (slow) hydration rate for UO2(+) when stored in the ion trap. To account for the production of the hydrated product, a reductive elimination reaction involving reactive collisions with water in the ion trap is proposed.     

NMR shielding calculations across the periodic table: diamagnetic uranium compounds. 2. Ligand and metal NMR

In this and a previous article (J. Phys. Chem. A 2000, 104, 8244), the range of application for relativistic density functional theory (DFT) is extended to the calculation of nuclear magnetic resonance (NMR) shieldings and chemical shifts in diamagnetic actinide compounds. Two relativistic DFT methods are used, ZORA ("zeroth-order regular approximation") and the quasirelativistic (QR) method. In the given second paper, NMR shieldings and chemical shifts are calculated and discussed for a wide range of compounds. The molecules studied comprise uranyl complexes, [UO(2)L(n)](+/-)(q); UF(6); inorganic UF(6) derivatives, UF(6-n)Cl(n), n = 0-6; and organometallic UF(6) derivatives, UF(6-n)(OCH(3))(n), n = 0-5. Uranyl complexes include [UO(2)F(4)](2-), [UO(2)Cl(4)](2-), [UO(2)(OH)(4)](2-), [UO(2)(CO(3))(3)](4-), and [UO(2)(H(2)O)(5)](2+). For the ligand NMR, moderate (e.g., (19)F NMR chemical shifts in UF(6-n)Cl(n)) to excellent agreement [e.g., (19)F chemical shift tensor in UF(6) or (1)H NMR in UF(6-n)(OCH(3))(n)] has been found between theory and experiment. The methods have been used to calculate the experimentally unknown (235)U NMR chemical shifts. A large chemical shift range of at least 21,000 ppm has been predicted for the (235)U nucleus. ZORA spin-orbit appears to be the most accurate method for predicting actinide metal chemical shifts. Trends in the (235)U NMR chemical shifts of UF(6-n)L(n) molecules are analyzed and explained in terms of the calculated electronic structure. It is argued that the energy separation and interaction between occupied and virtual orbitals with f-character are the determining factors.