A phenolate-induced trans influence: Crystallographic evidence for unusual asymmetric coordination of an α-diimine in ternary complexes of iron(III) possessing biologically relevant hetero-donor N-centered tripodal ligands

Musa S. Shongwe, Catherine H. Kaschula, Michael S. Adsetts, Eric W. Ainscough, Andrew M. Brodie, Michael J. Morris

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Abstract

Three mononuclear ternary complexes of iron(III) with an α-diimine (bipy or phen) and a derivative of N,N-bis(2-hydroxybenzyl)glycinate (L 3-) have been synthesized and characterized by magnetic susceptibility measurements, electron paramagnetic resonance (EPR) spectroscopy, vibrational spectroscopy, and electronic absorption spectroscopy. Single-crystal X-ray structure determinations of the pseudo-octahedral complexes [Fe(bipy)L]·MeCN [L = (3,5-Br2)-L3- or (5,3-Cl,Me)-L3-] revealed a considerable and consistent distortion in the coordination of bipy to iron(III) attributable largely to electronic effects. In both crystal structures, the Fe-Npyridyl bond Irans to the phenolate oxygen is 0.133 Å longer than the other one positioned trans to the tertiary amine nitrogen, a relatively weaker donor. This coordination behavior of bipy is of structural interest and has not been observed previously for iron(III). The electronic and EPR spectra of the compounds [Fe(L′-L′)L]·MeCN (L′-L′ = bipy or phen) are consistent with the spin state of the central metal atom (S = 5/2). The charge-transfer transitions arising from the strong interactions of the phenolate moieties with the ferric ion have been identified as phenolate (pπ) → iron(III) (dπ*) (λmax ≈ 500 nm, ε ≈ 3000 M-1 cm-1) and phenolate (pπ) → iron(III) (dσ*) (λmax ≈ 320 nm, ε ≈ 5200 M -1 cm-1). The presence of the phenolate moieties in the quadridentate hetero-donor tripodal ligands, H3L, lends these iron(III) ternary complexes the potential to model the specific metal-coordination, metal-substrate interactions, and physicochemical behaviors of several iron-tyrosinate proteins.

Original languageEnglish
Pages (from-to)3070-3079
Number of pages10
JournalInorganic Chemistry
Volume44
Issue number9
DOIs
Publication statusPublished - May 2 2005

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Iron
Ligands
iron
ligands
Metals
Paramagnetic resonance
electron paramagnetic resonance
metals
ferric ions
Vibrational spectroscopy
Magnetic susceptibility
Absorption spectroscopy
electronics
electronic spectra
spectroscopy
Amines
Charge transfer
amines
absorption spectroscopy
Nitrogen

ASJC Scopus subject areas

  • Inorganic Chemistry

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A phenolate-induced trans influence : Crystallographic evidence for unusual asymmetric coordination of an α-diimine in ternary complexes of iron(III) possessing biologically relevant hetero-donor N-centered tripodal ligands. / Shongwe, Musa S.; Kaschula, Catherine H.; Adsetts, Michael S.; Ainscough, Eric W.; Brodie, Andrew M.; Morris, Michael J.

In: Inorganic Chemistry, Vol. 44, No. 9, 02.05.2005, p. 3070-3079.

Research output: Contribution to journalArticle

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abstract = "Three mononuclear ternary complexes of iron(III) with an α-diimine (bipy or phen) and a derivative of N,N-bis(2-hydroxybenzyl)glycinate (L 3-) have been synthesized and characterized by magnetic susceptibility measurements, electron paramagnetic resonance (EPR) spectroscopy, vibrational spectroscopy, and electronic absorption spectroscopy. Single-crystal X-ray structure determinations of the pseudo-octahedral complexes [Fe(bipy)L]·MeCN [L = (3,5-Br2)-L3- or (5,3-Cl,Me)-L3-] revealed a considerable and consistent distortion in the coordination of bipy to iron(III) attributable largely to electronic effects. In both crystal structures, the Fe-Npyridyl bond Irans to the phenolate oxygen is 0.133 {\AA} longer than the other one positioned trans to the tertiary amine nitrogen, a relatively weaker donor. This coordination behavior of bipy is of structural interest and has not been observed previously for iron(III). The electronic and EPR spectra of the compounds [Fe(L′-L′)L]·MeCN (L′-L′ = bipy or phen) are consistent with the spin state of the central metal atom (S = 5/2). The charge-transfer transitions arising from the strong interactions of the phenolate moieties with the ferric ion have been identified as phenolate (pπ) → iron(III) (dπ*) (λmax ≈ 500 nm, ε ≈ 3000 M-1 cm-1) and phenolate (pπ) → iron(III) (dσ*) (λmax ≈ 320 nm, ε ≈ 5200 M -1 cm-1). The presence of the phenolate moieties in the quadridentate hetero-donor tripodal ligands, H3L, lends these iron(III) ternary complexes the potential to model the specific metal-coordination, metal-substrate interactions, and physicochemical behaviors of several iron-tyrosinate proteins.",
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T2 - Crystallographic evidence for unusual asymmetric coordination of an α-diimine in ternary complexes of iron(III) possessing biologically relevant hetero-donor N-centered tripodal ligands

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AU - Kaschula, Catherine H.

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AB - Three mononuclear ternary complexes of iron(III) with an α-diimine (bipy or phen) and a derivative of N,N-bis(2-hydroxybenzyl)glycinate (L 3-) have been synthesized and characterized by magnetic susceptibility measurements, electron paramagnetic resonance (EPR) spectroscopy, vibrational spectroscopy, and electronic absorption spectroscopy. Single-crystal X-ray structure determinations of the pseudo-octahedral complexes [Fe(bipy)L]·MeCN [L = (3,5-Br2)-L3- or (5,3-Cl,Me)-L3-] revealed a considerable and consistent distortion in the coordination of bipy to iron(III) attributable largely to electronic effects. In both crystal structures, the Fe-Npyridyl bond Irans to the phenolate oxygen is 0.133 Å longer than the other one positioned trans to the tertiary amine nitrogen, a relatively weaker donor. This coordination behavior of bipy is of structural interest and has not been observed previously for iron(III). The electronic and EPR spectra of the compounds [Fe(L′-L′)L]·MeCN (L′-L′ = bipy or phen) are consistent with the spin state of the central metal atom (S = 5/2). The charge-transfer transitions arising from the strong interactions of the phenolate moieties with the ferric ion have been identified as phenolate (pπ) → iron(III) (dπ*) (λmax ≈ 500 nm, ε ≈ 3000 M-1 cm-1) and phenolate (pπ) → iron(III) (dσ*) (λmax ≈ 320 nm, ε ≈ 5200 M -1 cm-1). The presence of the phenolate moieties in the quadridentate hetero-donor tripodal ligands, H3L, lends these iron(III) ternary complexes the potential to model the specific metal-coordination, metal-substrate interactions, and physicochemical behaviors of several iron-tyrosinate proteins.

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