부산대학교 도서관

The energy distributions and the properties of the lower vacant electronic states in cobalt and nickel tetraphenylporphyrin complexes CoTPP and NiTPP are studied by X-ray absorption spectroscopy. Quasimolecular analysis of the experimental absorption spectra measured in the region of the 2p and 1s ionization thresholds of complexing metal atoms, as well as the 1s thresholds of ligand atoms (nitrogen and carbon), is based on the comparison of the corresponding spectra with each other and with the spectra of the simplest nickel porphyrin NiP. It has been established that, despite a general similarity of the spectra of nitrogen and carbon in CoTPP and NiTPP, the fine structure of the 2p and 1s absorption spectra of cobalt and nickel atoms are radically different. The observed differences in the spectra of cobalt and nickel are associated with the features of the energy distribution of vacant 3d electron states. The presence in CoTPP of the partially filled valence 3d[b.sub.2g] molecular orbital (MO) results in the appearance in the cobalt spectra of a low-energy band, which is absent in the spectrum of nickel in NiTPP and leads to a doublet structure of transitions to [b.sub.1g] and eg MOs due to the exchange interaction between 3d electrons in partially filled 3d[b.sub.2g] and 3d[b.sub.1g] or 3[d.sub.eg] MOs. The spectrum of vacant states in CoTPP differs from that in NiTPP also due to the smaller energy distance between 3d[b.sub.1g] and [e.sub.g] MOs and the different positions of nonbonding MOs with the C2p character of the porphine ligand. DOI: 10.1134/S1063783418030307
1. INTRODUCTION Porphyrins of transition metal atoms attract great scientific and technological interest because of their key role in a number of biochemical processes [1, 2] and the possibilities of [...]