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Electronic structure of Ni(II) porphyrins and phthalocyanine studied by soft X-ray absorption spectroscopy

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Author

  • S. A. Krasnikov
  • Alexei Preobrajenski
  • N. N. Sergeeva
  • M. M. Brzhezinskaya
  • M. A. Nesterov
  • A. A. Cafolla
  • M. O. Senge
  • A. S. Vinogradov

Summary, in English

Investigations of chemical bonding and electronic structure features for polycrystalline Ni(II) phthalocyanine (NiPc), Ni(II) tetrabenzoporphyrin (NiTBP), Ni(II) 2,3,7,8,12,13,17,18-octaethylporphyrin (NiOEP), Ni(II) 5,10,15,20-tetraisobutylporphyrin (NiTiBuP), Ni(II) 5,15-diphenylporphyrin (NidPP) and Ni(II) 5,15-diisobutylporphyrin (NidiBuP) have been performed by means of high-resolution soft X-ray absorption spectroscopy. It has been found that the low-lying unoccupied electron states in nickel porphyrins are mainly generated by the NiN4 quasi-molecule: the lowest empty state is the weakly antibonding molecular orbital (MO) of sigma b(1g), symmetry with nearly pure Ni 3d(x2-y2) character, while the next empty state is the e(g) MO, which has a hybridized Ni 3d pi-N 2p pi character and reflects pi chemical bonding (pi-back-donation) between nickel and neighbouring nitrogen atoms of the pyrrole rings. The differences observed in the Ni 2p spectra of nickel porphyrins and phthalocyanines indicate a limited usefulness of the NiN4 quasi-molecule and a need for its extension to the whole porphyrin (phthalocyanine) macrocycle. As a result, the differences in the Ni 2p spectra of the complexes and in their electronic structure are associated with a torsion of the opposite pyrrole ring planes (NiOEP, NiTiBuP) and the presence of N atoms in meso positions (NiPc). These conclusions are further confirmed by a comparative analysis of the Ni 2p and N Is absorption spectra for NiPc and NiOEP. (c) 2007 Elsevier B.V. All rights reserved.

Department/s

Publishing year

2007

Language

English

Pages

318-324

Publication/Series

Chemical Physics

Volume

332

Issue

2-3

Document type

Journal article

Publisher

Elsevier

Topic

  • Natural Sciences
  • Physical Sciences

Keywords

  • x-ray absorption
  • electronic structure
  • phthalocyanine
  • porphyrin
  • spectroscopy
  • NEXAFS

Status

Published

ISBN/ISSN/Other

  • ISSN: 0301-0104