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Four-coordinate iron(II) porphyrinates: electronic configuration change by intermolecular interaction.

ABSTRACT: The syntheses and structures of three four-coordinate iron(II) porphyrinates are reported. The three derivatives are tetraarylporphyrin species, where the aryl is either phenyl, p-methylphenyl, or p-methoxyphenyl. One of these derivatives, that of tetraphenylporphyrin, Fe(TPP), is a new crystalline phase that is distinct from the earlier reported phase (Collman, J. P.; et al. J. Am. Chem. Soc. 1975, 97, 2676). This new phase of Fe(TPP) has a very saddled porphyrin core; the prior phase was ruffled. The iron atom has close interactions (approximately 3.10 A) with two pyrrole Cb-Cb bonds above and below the porphyrin plane. Mössbauer spectra and magnetic susceptibility measurements, different for the two phases, provide strong evidence that the two phases of Fe(TPP) have distinct electronic structures that originate from intermolecular interactions.

SUBMITTER: Hu C

PROVIDER: S-EPMC2515358 | biostudies-literature | 2007 Feb

REPOSITORIES: biostudies-literature

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Four-coordinate iron(II) porphyrinates: electronic configuration change by intermolecular interaction.

Hu Chuanjiang C Noll Bruce C BC Schulz Charles E CE Scheidt W Robert WR

Inorganic chemistry 20070201 3

The syntheses and structures of three four-coordinate iron(II) porphyrinates are reported. The three derivatives are tetraarylporphyrin species, where the aryl is either phenyl, p-methylphenyl, or p-methoxyphenyl. One of these derivatives, that of tetraphenylporphyrin, Fe(TPP), is a new crystalline phase that is distinct from the earlier reported phase (Collman, J. P.; et al. J. Am. Chem. Soc. 1975, 97, 2676). This new phase of Fe(TPP) has a very saddled porphyrin core; the prior phase was ruffl ...[more]

PMID: 17257003

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Project description:The electronic structures of the four- and five-coordinate aryl-substituted bis(imino)pyridine iron dinitrogen complexes, ((iPr)PDI)FeN(2) and ((iPr)PDI)Fe(N(2))(2) ((iPr)PDI = 2,6-(2,6-(i)Pr(2)-C(6)H(3)-N=CMe)(2)C(5)H(3)N), have been investigated by a combination of spectroscopic techniques (NMR, Mössbauer, X-ray Absorption and X-ray Emission) and DFT calculations. Homologation of the imine methyl backbone to ethyl or isopropyl groups resulted in the preparation of the new bis(imino)pyridine iron dinitrogen complexes, ((iPr)RPDI)FeN(2) ((iPr)RPDI = 2,6-(2,6-(i)Pr(2)-C(6)H(3)-N=CR)(2)C(5)H(3)N; R = Et, (i)Pr), that are exclusively four coordinate both in the solid state and in solution. The spectroscopic and computational data establish that the ((iPr)RPDI)FeN(2) compounds are intermediate spin ferrous derivatives (S(Fe) = 1) antiferromagnetically coupled to bis(imino)pyridine triplet diradical dianions (S(PDI) = 1). While this ground state description is identical to that previously reported for ((iPr)PDI)Fe(DMAP) (DMAP = 4-N,N-dimethylaminopyridine) and other four-coordinate iron compounds with principally ?-donating ligands, the d-orbital energetics determine the degree of coupling of the metal-chelate magnetic orbitals resulting in different NMR spectroscopic behavior. For ((iPr)RPDI)Fe(DMAP) and related compounds, this coupling is strong and results in temperature independent paramagnetism where a triplet excited state mixes with the singlet ground state via spin orbit coupling. In the ((iPr)RPDI)FeN(2) family, one of the iron SOMOs is essentially d(z2) in character resulting in poor overlap with the magnetic orbitals of the chelate, leading to thermal population of the triplet state and hence temperature dependent NMR behavior. The electronic structures of ((iPr)RPDI)FeN(2) and ((iPr)PDI)Fe(DMAP) differ from ((iPr)PDI)Fe(N(2))(2), a highly covalent molecule with a redox non-innocent chelate that is best described as a resonance hybrid between iron(0) and iron(II) canonical forms as originally proposed in 2004.

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Four-coordinate iron(II) porphyrinates: electronic configuration change by intermolecular interaction.

Publications

Four-coordinate iron(II) porphyrinates: electronic configuration change by intermolecular interaction.

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