title: A phenolate-induced trans influence: crystallographic evidence for unusual asymmetric coordination of an alpha-diimine in ternary complexes of iron(III) possessing biologically relevant hetero-donor N-centered tripodal ligands.
abstract: Three mononuclear ternary complexes of iron(III) with an alpha-diimine (bipy or phen) and a derivative of N,N-bis(2-hydroxybenzyl)glycinate (L3-) 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] x 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-N(pyridyl) bond trans to the phenolate oxygen is 0.133 A 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] x 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 (p(pi)) --> iron(III) (d(pi*)) (lambda(max) approximately 500 nm, epsilon approximately 3000 M(-1) cm(-1)) and phenolate (p(pi)) --> iron(III) (d(sigma*) (lambda(max) approximately 320 nm, epsilon approximately 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.
authors.affiliation: Department of Chemistry, College of Science, Sultan Qaboos University, P.O. Box 36, Al-Khod 123, Muscat, Sultanate of Oman. musa@squ.edu.om
authors.forename: Musa S
authors.initials: MS
authors.lastname: Shongwe
authors.forename: Catherine H
authors.initials: CH
authors.lastname: Kaschula
authors.forename: Michael S
authors.initials: MS
authors.lastname: Adsetts
authors.forename: Eric W
authors.initials: EW
authors.lastname: Ainscough
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Brodie
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Morris
mesh_terms: D002384:Catalysis; D018360:Crystallography, X-Ray; D049308:Dioxygenases / Q000737:chemistry* / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D005290:Ferric Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D007202:Indicators and Reagents; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D010636:Phenols / Q000737:chemistry; D013055:Spectrophotometry, Infrared
chemical_list: D005290:Ferric Compounds; D007202:Indicators and Reagents; D008024:Ligands; D010636:Phenols; D007501:Iron; D049308:Dioxygenases