(TAML)FeIV=O Complex in Aqueous Solution: Synthesis and Spectroscopic and Computational Characterization

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• 作者：Arani Chanda ; Xiaopeng Shan ; Mrinmoy Chakrabarti ; W. Chadwick Ellis ; Delia L. Popescu ; Filipe Tiago de Oliveira ; Dong Wang ; Lawrence Que Jr. ; Terrence J. Collins ; Eckard Mü ; nck ; Emile L. Bominaar
• 刊名：Inorganic Chemistry
• 出版年：2008
• 出版时间：May 5, 2008
• 年：2008
• 卷：47
• 期：9
• 页码：3669 - 3678
• 全文大小：604K
• 年卷期：v.47,no.9(May 5, 2008)
• ISSN：1520-510X

文摘

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, [Fe^IV(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*Fe^IV−O−Fe^IVB*]²⁻ (3), with a pK_a near 10. In zero field, the Mössbauer spectrum of 2 exhibits a quadrupole doublet with ΔE_Q = 3.95(3) mm/s and δ = −0.19(2) mm/s, parameters consistent with a S = 1 Fe^IV state. Studies in applied magnetic fields yielded the zero-field splitting parameter D = 24(3) cm⁻¹ together with the magnetic hyperfine tensor A/g_nβ_n = (−27, −27, +2) T. Fe K-edge EXAFS analysis of 2 shows a scatterer at 1.69 (2) Å, a distance consistent with a Fe^IVhttp://pubs.acs.org/images/entities/dbd_2.gif">O bond. DFT calculations for [Fe^IV(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.