Photoelectron spectra and electronic structure of boron diacetate formazanates

Sergey A Tikhonov; Andrey E Sidorin; Ilya S Samoilov; Aleksandr V Borisenko; Vitaliy I Vovna

doi:10.1016/j.saa.2020.118441

Photoelectron spectra and electronic structure of boron diacetate formazanates

Spectrochim Acta A Mol Biomol Spectrosc. 2020 Sep 5:238:118441. doi: 10.1016/j.saa.2020.118441. Epub 2020 May 5.

Authors

Sergey A Tikhonov¹, Andrey E Sidorin², Ilya S Samoilov³, Aleksandr V Borisenko⁴, Vitaliy I Vovna²

Affiliations

¹ Far Eastern Federal University, School of Natural Sciences, Vladivostok 690950, Russian Federation. Electronic address: allser@bk.ru.
² Far Eastern Federal University, School of Natural Sciences, Vladivostok 690950, Russian Federation.
³ Saint Petersburg State University, Department of Photonics, St. Petersburg 199034, Russian Federation.
⁴ Vladivostok Branch of Russian Customs Academy, Vladivostok 690034, Russian Federation.

PMID: 32403076
DOI: 10.1016/j.saa.2020.118441

Abstract

The electronic structure and cationic states of two 1,5-diphenylformazanes and two boron diacetate (B(OAc)₂) formazanates were modeled using the outer valence Green's function (OVGF) and density functional theory (DFT) methods. Comparison of data of the OVGF and ultraviolet photoelectron spectroscopy (UPS) methods made it possible to determine an effect of functional groups and complexing agents on energies of cationic states. Addition of NO₂-group at the γ-position of the chelate cycle causes stabilization of levels the five upper occupied molecular orbitals (MO) and destabilization of the bonding orbital π₃^Ph + π₃ level. The levels of MOs π₃^Ph-π₃ and n_- are stabilized due to influence of the complexing agent B(OAc)₂, with a difference in the shift of 0.67 eV. The ionization energies (I_n) changes for the π-orbitals of benzene rings are within the error of the OVGF method. Under methylation of phenyl groups, the differences between the calculated I_n, corresponding to the π-orbitals of aromatic substituents, are in good agreement with the experimental I_n shifts at transition from benzene to toluene. According to the OVGF method, in all the studied complexes the lowest unoccupied molecular orbital (LUMO) is localized mainly on the chelate cycle and has a strong acceptor character, which should contribute the low-lying charge-transfer electronic excitations. Moreover, an application of the DFT analog of the Koopmans' theorem with the BHHLYP and B2PLYP functionals made it possible to determine qualitatively a sequence of cationic states and energy intervals between them in the spectral range up to 10 eV. The DFT/wB97x/cc-pVTZ method data on the energy gap between the highest occupied molecular orbital (HOMO) and LUMO levels correlate with the OVGF/cc-pVTZ calculation results.

Keywords: Boron formazanate; Density functional theory; Electronic structure; Formazanate ligands; Outer-valence Green's function (OVGF) method; Photoelectron spectroscopy; UPS.