We report an ab initio quantum mechanical study on the interaction of M(n)()(+) cations (M(n)()(+) = La(3+), Eu(3+), Yb(3+), Sr(2+), and Na(+)) with model ligands L for lanthanide or actinide cations: several substituted amides, pyridines, and the phosphoryl-containing OPPh(3) ligand. The interaction energies DeltaE follow trends expected from the cation hardness and ligand basicity or softness in the amide series (primary < secondary-cis < secondary-trans < tertiary) as well as in the pyridine series (para-NO(2) < H < Me < NMe(2)). Among all ligands studied, OPPh(3) is clearly the best, while the (best) tertiary amide binds lanthanides slightly less than the (best) pyridine-NMe(2) ligand. In the lanthanide 1:1 complexes, the energy differences DeltaDeltaE as a function of M(3+) (about 40 kcal/mol for all ligands) are less than DeltaDeltaE in the pyridine series (up to about 90 kcal/mol) where marked polarization effects are found. The conclusions are validated by a number of methodological investigations. In addition to optimal binding features, we also investigate the directionality of ion coordination to the ligands and the effect of counterions and stoichiometry on the structural, electronic and energetic features of the complexes. The results are discussed in the context of modeling complexes of lanthanide and actinide cations and compared to those obtained with analogous Na(+) and Sr(2+) complexes.

We report molecular dynamics studies on the interfacial distribution of ionic species of different size, shape and topology at a water/chloroform interface: hydrophilic K + Cl − , K + SCN − and K + Pic − ions, amphiphilic ammonium NTMA + cations and farnesylphosphate FPH − anions, tetrahedral hydrophobic AsPh 4 + and BPh 4 − ions, with different counterions. Contrasted distributions are observed. The K + Cl − and K + SCN − ions sit almost exclusively in the water phase, but SCN − is less 'repelled' than Cl − by the interface. The Pic − anions are partly adsorbed at the interface and dissolved in the water phase where they display remarkable p-stacking interactions. Amphiphilic NTMA + cations or FPH − anions adsorb and dilute at the interface. Less expected is the high surface activity of symmetrical AsPh 4 + and BPh 4 − ions, with marked counterion effects. The two ions fully adsorb at the interface in the AsPh 4 + BPh 4 − salt, while in the Na + BPh 4 − or AsPh 4 + Cl − salts, they display an equilibrium between the organic phase and the interface. Crossed comparisons between the different solutions reveal the important role of counterions on the distribution of a given ionic species. These results are discussed in relation to experimental data.

We report a molecular dynamics (MD) study on M3+ lanthanide (La3+, Eu3+, and Yb3+) cations in dry acetonitrile solution and in M(MeCN) n 3+ clusters (n = 1−15) where two classical force-field representations of the cations are compared, in conjunction with the OPLS model of acetonitrile. It is shown that a set of van der Waals cation parameters (set2) fitted from free energies of hydration overestimates the cation coordination numbers (CNs). Another set of parameters (set1), where the size of cations is scaled down by 21/6 (using the σ van der Waals value for R*) yields better results. Quantum mechanical calculations performed on M(MeCN) n 3+ aggregates (n = 1−9) demonstrate the importance of charge-transfer and polarization effects. They confirm the preferred coordination number of eight for Yb3+, the Yb(MeCN)8+1 3+ species with one MeCN molecule in the outer coordination sphere being somewhat more stable than Yb(MeCN)9 3+ D 3 h . Adding a polarization term for the 1−6−12 OPLS acetonitrile to the force field (set2 + pol) indeed markedly improves the calculated CNs. In all MD simulations, a remarkable dynamic feature is observed in the first solvation shell where the lifetime of acetonitrile molecules increases from Yb3+ to La3+, that is, inversely to the cation−solvent interaction energies and to the aqueous phase behavior. Rare-earth salts with ClO4 - and F3CSO3 - anions and the question of ion binding selectivity by L ligands (formation of ML 3 3+ complexes, where L is a pyridine−dicarboxamide ligand) in acetonitrile solution are investigated by free-energy perturbation simulations, comparing the set1, set2, and set2+pol models. It is found that selectivities are markedly determined by the change in solvation-free energies of the uncomplexed cations, with pronounced counterion effects. The two simplest models (set1 or set2 without polarization) predict the correct order of complexation (Yb3+ > Eu3+ > La3+), whereas addition of polarization contribution leads to the inverse order, because of overestimation of the cation−anion interactions in the salt solutions.