The first water coordination sphere of lanthanide(<scp>iii</scp>) motexafins (Ln-Motex²⁺, Ln = La, Gd, Lu) and its effects on structures, reduction potentials and UV-vis absorption spectra. Theoretical studies

Abstract

Density functional calculations have been performed to study selected hydrated lanthanide(iii) motexafins (Ln-Motex²⁺, Ln = La, Gd, Lu) by using energy-consistent 4f-in-core lanthanide pseudopotentials to include the major relativistic effects due to the heavy metals. The maximum number (n) of water molecules bound strongly to [Ln-Motex]²⁺ (Ln = La, Gd, Lu) was determined to be 6 by calculating the change of the Gibbs energies for the reactions [Ln-Motex(H₂O)_n]²⁺ + H₂O → [Ln-Motex(H₂O)_n+1]²⁺. The number of water molecules coordinated directly to Ln³⁺ was found to be 3 for La, and 2 for Gd and Lu. The explicit treatment of the tightly bound water molecules in [Ln-Motex(H₂O)₆]²⁺ in combination with the COSMO solvation model yielded calculated reduction potentials and UV-vis absorption spectra in good agreement with available experimental data.