Relativistic density functional study on uranium(IV) and thorium(IV) oxide clusters of zonohedral geometry.

Free and ligated oxide clusters of thorium(IV) and uranium(IV) were studied with density functional theory using all-electron scalar relativistic method, as well as energy-consistent relativistic f-in-core pseudopotentials. The main driving force for the cluster formation is the sintering of the dioxoactinide moieties, which is more favorable for thorium(IV) than for uranium(IV) because, for the latter, a penalty for bending of the uranyl(IV) is to be paid. We assumed that the rhombic structural motif that exists already in the (AnO(2))(2) dimer could be a guide to explaining the preference for the existing An(6)O(8)-type clusters.

Theoretical study of the reduction of uranium(VI) aquo complexes on titania particles and by alcohols.

To provide insights into the adsorption and photoreduction of uranium(VI) on TiO(2), we have studied the structural and electronic properties of uranium(VI) aquo complexes adsorbed on stoichiometric and defected TiO(2) surfaces and nanoparticles. Plane wave calculations with the pure PBE density functional and the PBE+U approach were used to study U(VI) complexes on a periodic rutile (110) slab. In addition, a nanoparticulate Ti(38)O(76) cluster was used to simulate anatase nanoparticles.

Oxidative nucleophilic substitution of hydrogen in the sapphyrin dioxouranium(VI) complex: a relativistic DFT study.

A potentially trianionic expanded porphyrin ligand, sapphyrin does not form a 1:1 complex with the uranyl cation. However, in the presence of methanol, a complex of uranyl and meso-methoxy-substituted iso-sapphyrin is formed [Burrel et al. J.

Stability of Hydrocarbons of the Polyhedrane Family Containing Bridged CH Groups: A Case of Failure of the Colle-Salvetti Correlation Density Functionals.

DFT-computed energies of polyhedric hydrocarbons, such as dodecahedrane C20H20, its smaller analogs C16H16 and C12H12, and the larger C24H24, estimated in comparison with corresponding isomeric hydrocarbons, vary widely with the choice of the density functional. In particular, large discrepancies were observed with the functionals that are based on the B88 (as well as G96, B86) exchange and the LYP (as well as OP) correlation parts. The problem is not related to the presence of the smaller cyclopropane rings in the C12H12 polyhedrane, for its hydrogenated products do show similar errors; moreover, the larger dodecahedrane that is free from the Bayer strain shows a similar trend.

Performance of the Empirical Dispersion Corrections to Density Functional Theory: Thermodynamics of Hydrocarbon Isomerizations and Olefin Monomer Insertion Reactions.

Most of the commonly used approximate density functionals have systematic errors in the description of the stability of hydrocarbons. This poses a challenge for the realistic modeling of reactions involving hydrocarbons, such as olefin polymerization. Practical remedies have been proposed, including the application to usual black-box DFT of additional empirical correction CR(-6) terms for the van der Waals interaction (termed DFT-D), or introducing additional pseudopotentials that introduce some medium-to-long-range attraction (C-Pot).

Binuclear uranium(VI) complexes with a "pacman" expanded porphyrin: computational evidence for highly unusual bis-actinyl structures.

On the basis of uranyl complexes reacting with a polypyrrolic ligand (H(4)L), we explored structures and reaction energies of a series of new binuclear uranium(VI) complexes using relativistic density functional theory. Full geometry optimizations on [(UO(2))(2)(L)], in which two uranyl groups were initially placed into the pacman ligand cavity, led to two minimum-energy structures. These complexes with cation-cation interactions (CCI) exhibit unusual coordination modes of uranyls: one is a T-shaped (T) skeleton formed by two linear uranyls {O(exo)=U(2)=O(endo)-->U(1)(=O(exo))(2)}, and another is a butterfly-like (B) unit with one linear uranyl coordinating side-by-side to a second cis-uranyl.

Theoretical actinide molecular science.

Interest in the chemistry of the early actinide elements (notably uranium through americium) usually results either from the nuclear waste problem or the unique chemistry of these elements that result from 5f contributions to bonding. Computational actinide chemistry provides one useful tool for studying these processes. Theoretical actinide chemistry is challenging because three principal axes of approximation have to be optimized.

Modeling K+ and Ag+ complexation by thiacalix[4]arene amides using DFT: the role of intramolecular hydrogen bonding.

Complexation of methyl-glycine-amide functionalized thiacalix[4]arene with K(+) and Ag(+) has been studied using density functional theory (DFT) in the gas phase. To account for the conformational possibilities of the ligand, the free ligand and its potassium complexes were subjected to global minima searches on the molecular mechanics (MM) level of theory with the OPLS (optimized potentials for liquid simulations) force field. For the free ligand, the order of the energies and geometries of the ligand conformers is in agreement between MM and DFT; however, the position of K(+) in the ligand's cavity was predicted differently by these methods.

Theoretical study of the oxygen exchange in uranyl hydroxide. An old riddle solved?

A multistep mechanism for the experimentally observed oxygen exchange [Inorg. Chem. 1999, 38, 1456] of UO2(2+) cations in highly alkaline solutions is suggested and probed computationally.

Tetramerization of 3-methyl-cyclopropene-3-carbonitrile: a novel CN-alder-ene reaction.

At elevated temperatures 3-methyl-cyclopropene-3-carbonitrile 1 was found to tetramerize giving compound 2 (3-methyl-2,3-bis(2-t-methyl-2-c-cyanocyclopropyl)-1-(2-t-methyl-2-c,3-c-dicyanocyclopropyl)-cyclopropene) in good yields. This is the first example of Alder-ene type oligomerization of a 3,3-disubstituted cyclopropene. On the basis of the product geometry and stereoselective character of the reaction, a mechanism of formation of 2 involving CN-Alder-ene reaction was proposed.

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 role of peripheral alkyl substituents: a theoretical study of substituted and unsubstituted uranyl isoamethyrin complexes.

Relativistic density functional theory has been applied to the uranyl(VI) and uranyl(V) complexes of unsubstituted (1) and dodeca-alkyl-substituted (2) isoamethyrin (hexaphyrin(1.0.1.

A density functional study of the various forms of UN4O12 containing uranyl nitrate.

In this paper we report the computational results of a density functional study of 73 UN4O12 isomers containing uranyl nitrate, UO2(NO3)2, as a component. The isomers are grouped into three categories and 19 types. Forty-four isomers of 14 types are dinitrogen tetroxide adducts of uranyl nitrate, UO2(NO3)2.

A comparative relativistic DFT and ab initio study on the structure and thermodynamics of the oxofluorides of uranium(IV), (V) and (VI).

All the possible uranium(VI, V, IV) oxides, fluorides and oxofluorides were studied theoretically by using density functional theory (DFT) in the generalised gradient approximation (GGA), and three different relativistic methods (all-electron scalar four component Dyall RESC method (AE), relativistic small-core ECPs, and zeroth order regular approximation ZORA). In order to test different correlation methods, for the two former relativistic methods hybrid DFT, and, for the AE method, MP2 molecular orbital calculations were performed as well. Single-point AE-CCSD(T) energies were calculated on MP2 geometries as well.

Relativistic density functional theory study of dioxoactinide(VI) and -(V) complexation with alaskaphyrin and related Schiff-base macrocyclic ligands.

Formation of complexes of alaskaphyrin 1, bi-pyen 2 and bi-tpmd 3 ligands with actinyl ions AnO2(n+), An = U, Np, Pu and n = 1, 2, was studied using density functional theory (DFT) within the scalar relativistic four-component approximation. The alaskaphyrin complexes of the uranyl are predicted to have a bent conformation, in contrast to the experimentally available X-ray data. This deviation is likely due to crystal packing effects.

Density functional studies of actinyl aquo complexes studied using small-core effective core potentials and a scalar four-component relativistic method.

The title compounds, [AnO(2)(H(2)O)(5)](n)(+), n = 1 or 2 and An = U, Np, and Pu, are studied using relativistic density functional theory (DFT). Three rather different relativistic methods are used, small-core effective core potentials (SC-ECP), a scalar four-component all-electron relativistic method, and the zeroeth-order regular approximation. The methods provide similar results for a variety of properties, giving confidence in their accuracy.