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

ASJC Scopus subject areas

  • Inorganic Chemistry

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