IONIC VERSUS COVALENT CHARACTER IN LANTHANIDE COMPLEXES - A HYBRID DENSITY-FUNCTIONAL STUDY

The geometric structures and harmonic vibrational frequencies of La, G d and Lu trihalides have been investigated by a hybrid density functio nal/Hartree-Fock approach coupled with a relativistic effective core p otential. The adequacy of this electronic protocol is confirmed by the fairly good agreement with experimental data and with those obtained by more expensive post-HF computations. A detailed analysis of the ele ctronic density has been performed using the natural bond localization procedure and its recent extension to natural electronic resonance th eory to understand the role of charge transfer in the bonding of lanth anide complexes. This approach underlines the role of electrostatic in teractions in the lanthanide-halogen bond, even if a charge transfer m echanism plays a role, especially in the more weakly bonded bromide an d iodide derivatives.