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Updated: May 31, 2026

Surface Functionalization of Metal-Organic Frameworks for Improved Moisture Resistance
Published on: September 5, 2018
Toward functional carboxylate-bridged diiron protein mimics: achieving structural stability and conformational
1Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
None:
A dinucleating macrocycle, H(2)PIM, containing phenoxylimine metal-binding units has been prepared. Reaction of H(2)PIM with [Fe(2)(Mes)(4)] (Mes = 2,4,6-trimethylphenyl) and sterically hindered carboxylic acids, Ph(3)CCO(2)H or Ar(Tol)CO(2)H (2,6-bis(p-tolyl)benzoic acid), afforded complexes [Fe(2)(PIM)(Ph(3)CCO(2))(2)] (1) and [Fe(2)(PIM)(Ar(Tol)CO(2))(2)] (2), respectively. X-ray diffraction studies revealed that these diiron(II) complexes closely mimic the active site structures of the hydroxylase components of bacterial multicomponent monooxygenases (BMMs), particularly the syn disposition of the nitrogen donor atoms and the bridging micro-η(1)η(2) and micro-η(1)η(1) modes of the carboxylate ligands at the diiron(II) centers. Cyclic voltammograms of 1 and 2 displayed quasi-reversible redox couples at +16 and +108 mV vs ferrocene/ferrocenium, respectively. Treatment of 2 with silver perchlorate afforded a silver(I)/iron(III) heterodimetallic complex, [Fe(2)(micro-OH)(2)(ClO(4))(2)(PIM)(Ar(Tol)CO(2))Ag] (3), which was structurally and spectroscopically characterized. Complexes 1 and 2 both react rapidly with dioxygen. Oxygenation of 1 afforded a (micro-hydroxo)diiron(III) complex [Fe(2)(micro-OH)(PIM)(Ph(3)CCO(2))(3)] (4), a hexa(micro-hydroxo)tetrairon(III) complex [Fe(4)(micro-OH)(6)(PIM)(2)(Ph(3)CCO(2))(2)] (5), and an unidentified iron(III) species. Oxygenation of 2 exclusively formed di(carboxylato)diiron(III) compounds, a testimony to the role of the macrocylic ligand in preserving the dinuclear iron center under oxidizing conditions. X-ray crystallographic and (57)Fe Mössbauer spectroscopic investigations indicated that 2 reacts with dioxygen to give a mixture of (micro-oxo)diiron(III) [Fe(2)(micro-O)(PIM)(Ar(Tol)CO(2))(2)] (6) and di(micro-hydroxo)diiron(III) [Fe(2)(micro-OH)(2)(PIM)(Ar(Tol)CO(2))(2)] (7) units in the same crystal lattice. Compounds 6 and 7 spontaneously convert to a tetrairon(III) complex, [Fe(4)(micro-OH)(6)(PIM)(2)(Ar(Tol)CO(2))(2)] (8), when treated with excess H(2)O.
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