Photoelectron spectra and electronic structure of nitrogen-containing chelate boron complexes

Abstract

A brief review of the results of studying some classes of nitrogen-containing chelate boron complexes by ultraviolet photoelectron spectroscopy and density functional theory is reported. The quantum chemical modeling of the substitution effects of a complexing agent, heteroatoms, and functional groups in α, β, and γ positions of the chelate ring allowed us to establish the features of the electronic structure of the studied complexes. It is found that the substitution of heteroatoms in the chelate ring has no substantial influence on the structure of the highest occupied molecular orbital (HOMO). In imidoylamidinate complexes, as opposed to formazanates and β-diketonates, there is no noticeable mixing of π orbitals of the chelate and benzene rings. In condensed nitrogen heterocycles the HOMO is stabilized by 0.2-0.3 eV and π orbitals of the benzene ring are stabilized by 0.8-1.2 eV. The HOMO of substituted aza-boron-dipyridomethene correlates with anthracene and acridine π₇ orbitals, which causes the fine structure of the first band. It is shown that in an energy range below 11 eV the calculated results reproduce well the energy gaps between the ionization states of the complexes.