[en] Poly-pyridines have been studied in our laboratories as selective extractants of actinides(III) versus lanthanides(III) using a synergistic mixture with aliphatic carboxylic acids. Our aim in this study was, using theoretical chemistry, to better understand the actinide and lanthanide trivalent cations complexation with poly-pyridines. Molecular dynamics (MD) simulations have been performed for timescales between 100 and 500 ps using the AMBER software. These calculations are related to: (i) the gas phase and (ii) water solutions, with an explicit representation of the solvent. The present work call for further investigations concerning for example, (i) the effect of an organic solvent on ter-pyridines free and complexed, (ii) the description of the interaction potential (polarisation, charge transfer...), or (iii) the competition between M3+ ions and the protons for poly-pyridine complexation sites. (K.A.)

[en] The optimization of the management of radioactive wastes requires the separation of various radionuclides. Different processes are used: Purex, Diamex and Sanex. The challenge is to find new molecules able to select and extract actinides from lanthanides. Theoretical chemistry plays a more and more important role in this quest. Quantum chemistry allows the understanding of the electronic structure of molecules and of the interactions between extractive molecules and the elements to be extracted. Molecular dynamics gives the description of complex compounds like the solutions in which extracting reactions take place. These 2 tools of theoretical chemistry are complementary and are backed by important development in computer codes. (A.C.)

[en] This poster presents molecular dynamics simulations performed to study ter-pyridine and bis-triazinyl-pyridine with lanthanide cations for the gas phase and for water solution. Different counter-ions have been tested in order to assess their influence on complexes structures and stabilities in both phases. For stable complexes, Gibbs free energy calculations have been achieved to estimate the selectivity of these complexes towards the lanthanide cations. Finally, some tests have been done adding a polarization term in the potential energy in order to have a more precise description of interaction energies. (authors)

[en] 2-(2-Ethoxyethyl)-N,N,N'N'-tetraethylmalondiamide (TEEEMA, C₁₅H₃₀N₂O₃) reacts with lanthanum(III) nitrate to give the title complex, [La(NO₃)₃(TEEEMA)₂], in which the two carboxyl functions of each TEEEMA ligand are bonded to the metal ion together with three bidentate nitrate ions. This structure establishes that the ether O atom of the central chain of TEEEMA is not bonded to the metal ion, at least in the solid state. The coordination environment geometry is different from that of the lanthanum complex of N,N,N',N'-tetraethylmalondiamide (TEMA). (orig.)

[en] The structures and interaction energies of Ln³⁺(NO₃^-)n complexes have been studied using ab initio Hartree-Fock method for La³⁺, Eu³⁺ and Lu³⁺ cations with one to three nitrates in gas phase. The interaction energy between one cation and one bidentate nitrate is 20 to 30 kCal/mol greater than that with one monodentate nitrate. This value is quite lower than the interaction between a cation and one water molecule (about 90 kCal/mol), which could come and complete the hydration sphere of the cation when nitrate's coordination-type moves from bidentate to monodentate. The first studies on these systems with five water molecules in the hydration sphere show changes in the coordination type of nitrates or moves of water molecules in the second sphere. (authors)

[en] The spectroscopic and thermodynamic properties of the molecules MC₂₈ (M = Ce, Th, Pa⁺, U²⁺, Pu⁴⁺) are calculated using density functional theory. The systems have considerable energetic stability. It is shown that the actinide cases can be classified as '32-electron' systems, using the bonding s-, p-, d-, and f-type orbitals of the central metal. The rest of the valence molecular orbitals have purely carbon character. (authors)

[en] In this work, it has been found that the 6p valence band of the recently discovered icosahedral [Pb₁₂]^2- shell forms a perfect partner for the 5f shell of an enclosed actinide atom such as plutonium. Detailed DFT calculations suggest that the system is viable. It could, on good grounds, be characterized as a 32e system. Experimental results are described into details. (O.M.)

[en] Complete text of publication follows: The 18-electron principle goes back to Langmuir [2]. For its history and interpretation, see the recent paper [3]. Formally it would correspond to fully occupying at a central atom its ns, np and (n-1)d orbitals. For early 5f-elements the f-shell becomes chemically available and remains so until about Am. Theoretically it could be filled with 14 further electrons, bringing the total to 32, a theoretical possibility already evoked by Langmuir [2]. How far towards that limit can one go? Thorocene, Th(C₈H₈)₂, was classified as a '20e' case [3]. In the 'metalloactinyl' compounds, like the linear IrThIr^2-, one could potentially reach '24e' [4]. We now find that the 6p valence band of the recently discovered icosahedral [Pb₁₂]^2- shells forms a perfect partner for the 5f shell of an enclosed actinide atom, like plutonium. Detailed DFT calculations suggest that the system is viable. It could be on good grounds characterised as a '32e' system. The calculated molecular geometries, an orbital analysis and a bonding energy analysis in term of Morokuma-type decomposition will be presented for [Pb₁₂]^2- and [M*Pb₁₂]^x- with M=Yb, Th, U, Np, Pu, Am, Cm. The orbital-energy spectra and the densities of states for [Pb₁₂]^2-, [An*Pb₁₂]^x- (An=Pu, Am, Cm) will be given. Finally we will show for [Pu*Pb12] an ELF distribution, clearly demonstrating the radial bonds. References: [1] J.-P. Dognon, C. Clavaguera, P. Pyykko, Angew. Chem. Int. Ed. 2007, 46, 1- 5 [2] I. Langmuir, Science 1921, 54, 59-67, this paper mentions the 8, 18 and 32-electron closed shells and uses on pp. 65-66 Fe(CO)₅, Ni(CO)₄ and Mo(CO)₆ as examples on 18e. [3] P. Pyykko, J. Organomet. Chem. 2006, 691, 4336-4340 [4] P. Hrobarik, M. Straka, P. Pyykko, Chem. Phys. Lett. 2006, 431, 6-12

[en] The ground-state electronic structure of the cyanido complex [U(η⁸-C₈H₈)₂(CN)]^- as well as the thermodynamic properties and infrared spectrum are investigated using density functional theory including scalar relativistic effects. The complex is compared with the well known uranocene U(η⁸-C₈H₈)₂. Despite the broken symmetry, the gain in electrostatic interaction and a significant uranium-CN^- orbital interaction is sufficient to stabilize the bent CN^- complex with respect to uranocene. The formation of the CN^- complex is exothermic justifying the recently experimentally reported compound. (authors)

[en] The electronic structures, as well as spectroscopic and thermodynamic properties of the title PuM₁₂ clusters, are considered at the density functional theory level. In both cases, a Pu²⁺ ion is encapsulated in an icosahedral, stanna- or plumbaspherene M₁₂^2- cage. As suggested before for M=Pb, both systems are reported to follow a 32-electron principle for the central atom. (authors)