| Abstract
| - Recently, we reported the characterization of the S = 1/2 complex [FeV(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 [FeIII(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−FeIVB*]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 FeIVO 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.
- We report the synthesis and spectroscopic (Mössbauer, electronic absorption, and EXAFS), and computational (DFT) identification of complex [FeIV(O)B*]2−, where B* is a tetraamido macrocyclic ligand. The complex was prepared in aqueous solution at pH > 12 by oxidation of [FeIII(H2O)B*]−. At room temperature, [FeIV(O)B*]2− is in a reversible, pH-dependent equilibrium with dimeric species [B*FeIV−O−FeIVB*]2−, with a pKa near 10. A comparative analysis shows that the 57Fe hyperfine parameters of [FeIV(O)B*]2− give evidence for strong electron donation from B* to iron.
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