TY - JOUR

T1 - Electronic structure of Ni(II) porphyrins and phthalocyanine studied by soft X-ray absorption spectroscopy

AU - Krasnikov, S. A.

AU - Preobrajenski, A. B.

AU - Sergeeva, N. N.

AU - Brzhezinskaya, M. M.

AU - Nesterov, M. A.

AU - Cafolla, A. A.

AU - Senge, M. O.

AU - Vinogradov, A. S.

N1 - Copyright: Copyright 2007 Elsevier B.V., All rights reserved.

PY - 2007/2/14

Y1 - 2007/2/14

N2 - 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 σb1g symmetry with nearly pure Ni 3 dx2 - y2 character, while the next empty state is the eg MO, which has a hybridized Ni 3dπ-N 2pπ character and reflects π chemical bonding (π-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 1s absorption spectra for NiPc and NiOEP.

AB - 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 σb1g symmetry with nearly pure Ni 3 dx2 - y2 character, while the next empty state is the eg MO, which has a hybridized Ni 3dπ-N 2pπ character and reflects π chemical bonding (π-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 1s absorption spectra for NiPc and NiOEP.

KW - Back-donation

KW - Electronic structure

KW - NEXAFS

KW - Phthalocyanine

KW - Porphyrin

KW - X-ray absorption spectroscopy

UR - http://www.scopus.com/inward/record.url?scp=33846839181&partnerID=8YFLogxK

U2 - 10.1016/j.chemphys.2006.12.015

DO - 10.1016/j.chemphys.2006.12.015

M3 - Article

AN - SCOPUS:33846839181

VL - 332

SP - 318

EP - 324

JO - Chemical Physics

JF - Chemical Physics

SN - 0301-0104

IS - 2-3

ER -