(TAML)FeIV=O complex in aqueous solution: Synthesis and spectroscopic and computational characterization

Arani Chanda, Xiaopeng Shan, Mrinmoy Chakrabarti, W. Chadwick Ellis, Delia L. Popescu, Filipe Tiago De Oliveira, Dong Wang, Lawrence Que, Terrence J. Collins, Eckard Münck, Emile L. Bominaar

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Recently, we reported the characterization of the S = 1/2 complex [Fe V(O)B*]-, where B* belongs to a family of tetraamido macrocyclic ligands (TAMLs) whose iron complexes activate peroxides for environmentally useful applications. The corresponding one-electron reduced species, [FeIV(O)B*]2- (2), has now been prepared in >95% yield in aqueous solution at pH > 12 by oxidation of [Fe III(H2O)B*]- (1), with tert-butyl hydroperoxide. At room temperature, the monomeric species 2 is in a reversible, pH-dependent equilibrium with dimeric species [B*FeIV-O-Fe IVB*]2- (3), with a pKa near 10. In zero field, the Mössbauer spectrum of 2 exhibits a quadrupole doublet with ΔEQ = 3.95(3) mm/s and δ = -0.19(2) mm/s, parameters consistent with a S = 1 FeIV state. Studies in applied magnetic fields yielded the zero-field splitting parameter D = 24(3) cm-1 together with the magnetic hyperfine tensor A/gnβn = (-27, -27, +2) T. Fe K-edge EXAFS analysis of 2 shows a scatterer at 1.69 (2) Å, a distance consistent with a FeIV=O bond. DFT calculations for [FeIV(O)B*]2- reproduce the experimental data quite well. Further significant improvement was achieved by introducing hydrogen bonding of the axial oxygen with two solvent-water molecules. It is shown, using DFT, that the 57Fe hyperfine parameters of complex 2 give evidence for strong electron donation from B* to iron.

Original languageEnglish (US)
Pages (from-to)3669-3678
Number of pages10
JournalInorganic chemistry
Issue number9
StatePublished - May 5 2008


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