Quantum chemical study of Lniii(pyridine-dicarboxy-amide)1 complexes

Abstract

Quantum chemical simulations have been performed on Ln^III(pyridine-dicarboxy-amide)₁ complexes in order to describe the interaction between the lanthanide cations (La^III, Eu^III, and Lu^III) and the ligand (R₂R′₂PDA). In particular, the influence of substituents R (R₂R′₂ = H₄, Me₄, Ph₂Me₂, Ph₄) on the interaction between the cation and the R₄PDA ligand has been discussed. The substitution of H₄ by Me₄ on the ligand stabilizes the Ln^III–ligand interaction of 33 kcal mol⁻¹ (La^III) to 38 kcal mol⁻¹ (Lu^III), and the Ph₄ substitution of 69 kcal mol⁻¹ (La^III) and 75 kcal mol⁻¹ (Lu^III). Although the Ln^III(H₄PDA)₁ and Ln^III(Ph₄PDA)₁ complexes have a C_2v symmetry, the four methyl substituents reduce the symmetry of the complex to C_s, placing the cation out of the central pyridinyl plane. These results also emphasize that, for a given ligand, the lutetium complexes are more stable than the lanthanum complexes, which can be linked to the increasing experimental separation factors inside the lanthanide family.