Search

Bis-triazinyl pyridines (BTPs) exhibit solution selectivity for trivalent americium over lanthanides (Ln), the origins of which remain uncertain. Here, electrospray ionization was used to generate gas-phase complexes [ML3]3+, where M = La, Lu, or Am and L is EtBTP 2,6-bis(5,6-diethyl-1,2,4-triazin-3-yl)-pyridine. Collision-induced dissociation (CID) of [ML3]3+ in the presence of H2O yielded a protonated ligand [L(H)]+ and hydroxide [ML2(OH)]2+ or hydrate [ML(L-H)(H2O)]2+, where (L-H)- is a deprotonated ligand. Although solution affinities indicate stronger binding of BTPs toward Am3+ versus Ln3+, the observed CID process is contrastingly more facile for M = Am versus Ln. To understand the disparity, density functional theory was employed to compute potential energy surfaces for two possible CID processes, for M = La and Am. In accordance with the CID results, both the rate determining transition state barrier and the net energy are lower for [AmL3]3+ versus [LaL3]3+ and for both product isomers, [ML2(OH)]2+ and [ML(L-H)(H2O)]2+. More facile removal of a ligand from [AmL3]3+ by CID does not necessarily contradict stronger Am3+-L binding, as inferred from solution behavior. In particular, the formation of new bonds in the products can distort kinetics and thermodynamics expected for simple bond cleavage reactions. In addition to correctly predicting the seemingly anomalous CID behavior, the computational results indicate greater participation of Am 5f versus La 4f orbitals in metal-ligand bonding.

The ternary antimonide CeNiSb3 has been prepared from an Sb flux or from reaction of Ce, NiSb, and Sb above 1123K. It crystallizes in the orthorhombic space group Pbcm with Z=12 and lattice parameters a=12.6340(7)Å, b=6.2037(3)Å, and c=18.3698(9)Å at 193K. Its structure consists of buckled square nets of Sb atoms and layers of highly distorted edge- and face-sharing NiSb6 octahedra. Located between the ∞2[Sb] and ∞2[NiSb2] layers are the Ce atoms, in monocapped square antiprismatic coordination. There is an extensive network of Sb-Sb bonding with distances varying between 3.0 and 3.4Å. The structure is related to that of RECrSb3 but with a different stacking of the metal-centered octahedra. Resistivity measurements reveal a shallow minimum near 25K that is suggestive of Kondo lattice behavior, followed by a sharp decrease below 6K. © 2003 Elsevier Inc. All rights reserved.

The synthesis of the first molecular uranyl iodate [Na.sub.2]){U[O.sub.2][[IO.sub.3].sub.4])[H.sub.2]O} is presented. The concomitant formation of intermolecular hydrogen bonds and iodate...iodate interactions are instrumental in aligning the lone-pair of electrons on the iodate anions to yield the first polar uranyl iodate.

The reaction of U[O.sub.3] with Se[O.sub.2] in the presence of Sr[Cl.sub.2] x 6[H.sub.2]O and Sr[(OH).sub.2] x 8[H.sub.2]O in supercritical water at 425[degrees]C for 3 d results in the formation of the new strontium uranyl selenites, Sr[[(U[O.sub.2]).sub.3][(Se[O.sub.3]).sub.2][O.sub.2]] x 4[H.sub.2]O (1) and Sr[U[O.sub.2][(Se[O.sub.3]).sub.2]] (2). The single crystal X-ray structures of type 1 and type 2 were solved by direct methods and refined by full-matrix least-squares methods. Crystallographic data (193 K): (1), monoclinic, space group C2/m, a = 17.014(2), b = 7.0637(7), and c = 7.1084(7) [Angstrom], [beta] = 100.544(2)[degrees], Z = 2, R(F) = 0.0361 for 79 parameters with 1132 reflections with I > 2[sigma](I), w[R.sub.2] = 0.0998 for all data; (2), triclinic, space group P[bar 1], a = 5.6722(4), b = 6.7627(5), and c = 11.2622(8) [Angstrom], [alpha] = 104.698(1)[degrees], [beta] = 93.708(1)[degrees], [gamma] = 109.489(1)[degrees], Z = 2, R(F) = 0.0373 for 110 parameters with 1902 reflections with I > 2[sigma](I), w[R.sub.2] = 0.0856 for all data. The structure of type 1 contains two-dimensional [[sup.2.sub.[infinity]][[[(U[O.sub.2]).sub.3][(Se[O.sub.3]).sub.2] [O.sub.2]].sup.2-] sheets with the same topology as those found in guilleminite, Ba[[(U[O.sub.2]).sub.3][(Se[O.sub.3]).sub.2][O.sub.2] x 3[H.sub.2]O, and marthozite, Cu[[(U[O.sub.2]).sub.3][(Se[O.sub.3]).sub.2][O.sub.2]][([H.sub.2]O].sub.8]. [Sr.sup.2+] cations and [H.sub.2]O groups occur between the layers. In contrast, the structure of type 2 contains one-dimensional [[sup.1.sub.[infinity]][U[O.sub.2][(Se[O.sub.3]).sub.2]].sup.2-] ribbons with [Sr.sup.2+] cations residing between them. This compound is isostructural with its [Ca.sup.2+]-containing analog.

Research has been conducted on uranium(VI). The reactions of this compound with acidic aqueous chloride solutions have produced polymeric uranium(VI) compounds, and single crystals have been formed under hydrothermal conditions.

Research has been conducted on theuranyl tellurite system. The study of this system carried out via the structures, hydrothermal preparation and properties of different uranyl tellurites is presented.