On the calculation and interpretation of covalency in the intensity parameters of 4f-4f transitions in Eu3+ complexes based on the chemical bond overlap polarizability

The concepts of chemical bond overlap polarizability (αOP) and of specific ionic valence (υ) were used to characterize the Eu3+-ligating atom bonds in complexes. The underlying chemical bond properties, namely, bond distance, overlap integral, force constant, and the energy excitation, were successfully calculated for the Eu3+-ligating atom diatomic-like species under the influence of the molecular environment. The quantities αOP and υ were used to reshape and reinterpret the expressions of the forced electric dipole (FED) and the dynamic coupling (DC) mechanisms responsible for the intensity parameters of 4f-4f transitions. These parameters were calculated with this new approach for a series of Eu3+ complexes: [EuL3L′] with L=AIND, BIND, TTA, BTFA, FOD, ABSe, ABSeCl, DPM and L′=(H2O)2, NO3, DPbpy, DBSO, TPPO, Phen, for which the experimental intensity parameters and some E00 (=5D0→7F0) energies are available. Comparisons between the theoretical and experimental results suggest that this new methodology is reliable and an important step toward an approach to calculate the 4f-4f intensities free of adjustable parameters, which has been accomplished for complexes without aquo ligand.