Molecular dynamics simulations of lanthanide(iii) diphenyldimethylpyridinyl–dicarboxyamide complexes in water and in methanol: evidence for both first and second sphere complexes

Abstract

We report a molecular dynamics simulation study of lanthanide(III) diphenyldimethylpyridinyl-dicarboxyamide (Ph₂Me₂PDA) complexes in water and methanol, with nitrate (NO₃⁻) counter-ions. Depending on the cation size (La³⁺, Eu³⁺, and Lu³⁺) and on the number of PDA ligands initially located in the cation's first sphere of coordination, two opposite behaviors are observed. In the case of a 1∶3 cation∶ligand stoichiometry with nitrates far from the cation, the PDA ligands partially move in the second sphere for La³⁺ and Eu³⁺, whereas they remain in the first coordination sphere for the smaller cation. In the case of a 1∶2 cation∶ligand stoichiometry with nitrates coordinated to the cation, the PDA ligands remain tridentate for the larger cation (La³⁺), whereas they partly move to the second sphere for the smaller cations, without dissociation. In the case of second sphere ligands, solvent molecules located in the cation's first coordination sphere provide a H-bond bridge between the cation and the amidic oxygen of the ligand remaining in the second sphere.