Electronic structure of the [Ni(Salen)] complex studied by core-level spectroscopies

Abstract

The nature and structure of occupied and empty valence electronic states (molecular orbitals, MOs) of the [Ni(Salen)] molecular complex (NiO2N2C16H14) have been studied by means of X-ray photoemission and absorption...

The Valence Band Structure of the [Ni(Salen)] Complex: An Ultraviolet, Soft X-ray and Resonant Photoemission Spectroscopy Study

“…The low-energy a’ , a , b , and c bands are located in the UV PE spectrum of [Ni(Salen)] at the BE of 2.6, 3.8, 5.2, and 7.6 eV, respectively (see Figure 2 b and inset). It should be noted that this peak fitting is somewhat different in terms of peak energy positions from that previously proposed [ 14 ]. This low-BE region is characterized by a noticeably less intense and almost structureless energy distribution of the PE signal in the H 2 Salen spectrum.…”

“…As can be seen from Figure 2 , all the spectra are characterized by the a’–i bands, except for the UV PE spectrum for which the binding energy interval is somewhat smaller, due to the low value of the exciting photon energy. These bands are the result of the photoionization of the valence hybridized MOs of the complex, which are formed by the 3d and 4s AOs of the complexing Ni atom, as well as the 2p and 2s AOs of the ligand atoms (O, N, and C) [ 14 ]. It can be seen that the energy positions of the PE bands in the VB spectra remain unchanged as the energy of the exciting photons increases, while their absolute intensities decrease monotonically with an increase in photon energies hv from 75 to 848 eV.…”

“…The atomic structure of this complex is based on the complexing nickel atom which coordinates two oxygen and two nitrogen atoms of the ligand, forming an almost square-planar [NiO 2 N 2 ] coordination center ( Figure 1 ) [ 13 ]. An important feature of the [Ni(Salen)] complex is that it is diamagnetic with the total spin S = 0 in the ground state, due to the fact that all valence molecular orbitals (MOs) are completely filled [ 14 , 15 ]. This significantly simplifies acquiring detailed information about the electronic structure of this complex.…”

“…In reference [ 14 ], the characterization of the atomic and electronic structure of the [Ni(Salen)] complex was performed using NEXAFS and XPS, as well as density functional theory (DFT) calculations. It was found that the highest occupied MO (HOMO) in the valence band (VB) is mainly localized on the phenyl rings of the salen ligand at a binding energy (BE) of 2.9 eV.…”

“…This work is devoted to a detailed study of the electronic structure of the valence band of the monomeric [Ni(Salen)] complex and the role of the Ni 3d electrons in its formation using a combination of photoemission methods. In this respect, it is a development of the photoemission study of this valence band that was carried out in [ 14 ] using only two close energies of exciting photons (75 and 150 eV), which severely limits the reliability of the conclusions drawn. To obtain more reliable information, radiation with photon energies in a wide range from 21.2 to 848 eV is exited.…”