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(NH ) ] [Eu(DOTP)]·12.5H O and K [Eu(DOTP)]·11H O (DOTP = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis (methylenephosphonic acid)), were determined. The DOTP ligand is bonded to Eu via four O and four N atoms, filling thus eight coordination sites of Eu . The experimental structures of two [K Eu(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 4f configuration of the Eu ion have been calculated and compared with those derived from the experimental spectra. This enabled us to tentatively assign energy levels of the Eu 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.