Theoretical Study of Metal−Ligand Interaction in Sm(III), Eu(III), and
Tb(III) Complexes of Coumarin-3-Carboxylic Acid in the Gas Phase and
Solution
GeorgievaIvelina
TrendafilovaNatasha
J. A. AquinoAdélia
LischkaHans
2007
The interaction of lanthanide(III) cations (Ln(III) = Sm(III), Eu(III), and Tb(III)) with the deprotonated form of the
coumarin-3-carboxylic acid (<i>cca</i><i><sup>-</sup></i><sup></sup>) has been investigated by density functional theory (DFT/B3LYP) and confirmed
by reference MP2 and CCSD(T) computations. Solvent effects on the geometries and stabilities of the Ln(III)
complexes were computed using a combination of water clusters and a continuum solvation model. The following
two series of systems were considered: (i) Ln(<i>cca</i>)<sup>2+</sup>, Ln(<i>cca</i>)<sub>2</sub><sup>+</sup>, Ln(<i>cca</i>)<sub>3</sub> and (ii) Ln(<i>cca</i>)(H<sub>2</sub>O)<sub>2</sub>Cl<sub>2</sub>, Ln(<i>cca</i>)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>Cl, Ln(<i>cca</i>)<sub>3</sub>. The strength and character of the Ln(III)−<i>cca</i><i><sup>-</sup></i><sup></sup> bidentate bonding were characterized by calculated
Ln−O bond lengths, binding energies, ligand deformation energies, energy partitioning analysis, σ-donation
contributions, and natural population analyses. The energy decomposition calculations predicted predominant
electrostatic interaction terms to the Ln−<i>cca</i> bonding (ionic character) and showed variations of the orbital interaction
term (covalent contributions) for the Ln−<i>cca</i> complexes studied. Electron distribution analysis suggested that the
covalent contribution comes mainly from the interaction with the carboxylate moiety of <i>cca</i><sup>-</sup>.