The first example of ab initio calculations of f–f transitions for the case of [Eu(DOTP)]5− complex—experiment versus theory

Abstract

Crystal structures and photophysical properties (IR and UV-vis-NIR) of two compounds, [C(NH₂)₃]₅[Eu(DOTP)]·12.5H₂O and K₅[Eu(DOTP)]·11H₂O (DOTP = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis (methylenephosphonic acid)), were determined. The DOTP ligand is bonded to Eu³⁺via four O and four N atoms, filling thus eight coordination sites of Eu³⁺. The experimental structures of two [K₄Eu(DOTP)]⁻ clusters were used as a starting point for theoretical ab initio calculations based on a multireference wavefunction approach. Positions of the energy levels of the 4f⁶ configuration of the Eu³⁺ ion have been calculated and compared with those derived from the experimental spectra. This enabled us to tentatively assign energy levels of the Eu³⁺ ion. The relationship between calculated energies of excited states and Eu–N and Eu–O bond lengths was discussed with respect to the nephelauxetic effect.