Effects of solvents on the electron configurations of the low-spin dicyano[meso-tetrakis(2,4,6-triethylphenyl)porphyrinato]iron(III) complex: Importance of the C-H···N weak hydrogen bonding

Akira Ikezaki, Mikio Nakamura

Research output: Contribution to journalArticle

32 Citations (Scopus)

Abstract

There are two types of electron configurations, (dxy)2(dxz, dyz)3 and (dxz, dyz)4(dxy)1, in low-spin iron(III) porphyrin complexes. To reveal the solvent effects on the ground-state electron configurations, we have examined the 13C-and 1H-NMR spectra of low-spin dicyano[meso-tetrakis(2,4,6-triethylphenyl)porphyrinato] ferrate(III) in a variety of solvents, including protic, dipolar aprotic, and nonpolar solvents. On the basis of the NMR study, we have reached the following conclusions: (i) the complex adopts the ground state with the (dxz, dyz)4(dxy)1 electron configuration, the (dxz, dyz)4(dxy)1 ground state, in methanol, because the dorbitals are stabilized due to the O-H···N hydrogen bonding between the coordinated cyanide and methanol; (ii) the complex also exhibits the (dxz, dyz)4(dxy)1 ground state in nonpolar solvents, such as chloroform and dichloromethane, which is ascribed to the stabilization of the dorbitals due to the C-H···N weak hydrogen bonding between the coordinated cyanide and the solvent molecules; (iii) the complex favors the (dxz, dyz)4(dxy)1 ground state in dipolar aprotic solvents, such as DMF, DMSO, and acetone, though the (dxz, dyz)4(dxy)1 character is less than that in chloroform and dichloromethane; (iv) the complex adopts the (dxy)2(dxz, dyz)3 ground state in nonpolar solvents, such as toluene, benzene, and tetrachloromethane, because of the lack of hydrogen bonding in these solvents; (v) acetonitrile behaves like nonpolar solvents, such as toluene, benzene, and tetrachloromethane, though it is classified as a dipolar aprotic solvent. Although the NMR results have been interpreted in terms of the solvent effects on the ordering of the dxy and d orbitals, they could also be interpreted in terms of the solvent effects on the population ratios of two isomers with different electron configurations. In fact, we have observed the unprecedented EPR spectra at 4.2 K which contain both the axial- and large gmax-type signals in some solvents such as benzene, toluene, and acetonitrile. The observation of the two types of signals has been ascribed to the slow interconversion on the EPR time scale at 4.2 K between the ruffled complex with the (dxz, dyz)4(dxy)1 ground state and, possibly, the planar (or nearly planar) complex with the (dxy)2(dxz, dyz)3 ground state.

Original languageEnglish
Pages (from-to)2761-2768
Number of pages8
JournalInorganic Chemistry
Volume41
Issue number10
DOIs
Publication statusPublished - 2002 May 20

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

Fingerprint Dive into the research topics of 'Effects of solvents on the electron configurations of the low-spin dicyano[meso-tetrakis(2,4,6-triethylphenyl)porphyrinato]iron(III) complex: Importance of the C-H···N weak hydrogen bonding'. Together they form a unique fingerprint.

Cite this