Relaxation of Kohn–Sham orbitals of organometallic complexes during the approach of a nucleophilic reactant (or an electron approach): the case of [sal(ph)en]2 Zn complexes

Abstract

In a recent paper, the Lewis acidic character of a series of Zn-Sal(ph)en complexes was reviewed, using conceptual density functional theory descriptors to assess the acidic character. It was shown that the nature of the bridging diamine link in the Schiff base ligand controls this character that is mainly responsible for the coordination of the Zn2+, hence for the geometry of these complexes. However, the usual dual descriptor did exhibit significant weaknesses to retrieve the electrophilic part on the metal cation of the Zn-sal(ph)en complexes. Indeed, it is necessary to include the densities of the electronic excited states through the so-called state-specific dual descriptor. This procedure will allow us to recover successfully the appropriate reactivity of the studied complexes holding diamine bridges differing by flexible to semi-rigid and to rigid ranges. Nevertheless, the selection of the excited state allowing a meaningful description of the Lewis acidic is not a priori obtained from a direct identification of the Kohn–Sham (KS) orbitals involved in the excitation. The present work reports an analysis of the relaxation of the KS orbitals when a fraction of charge is added to a virtual orbital, and when an excitation is considered, while a fractional charge is transferred from an occupied orbital toward a virtual orbital.