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

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.