(TAML)FeIV O complex in aqueous solution: synthesis and spectroscopic and computational characterization.
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)(H 2O)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 (IV)B*] (2-) ( 3), with a p K a near 10. In zero field, the Mössbauer spectrum of 2 exhibits a quadrupole doublet with Delta E Q = 3.95(3) mm/s and delta = -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 nbeta n = (-27, -27, +2) T. Fe K-edge EXAFS analysis of 2 shows a scatterer at 1.69 (2) A, a distance consistent with a Fe (IV)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 (57)Fe hyperfine parameters of complex 2 give evidence for strong electron donation from B* to iron.
Chanda
Arani
A
Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
Shan
Xiaopeng
X
Chakrabarti
Mrinmoy
M
Ellis
W Chadwick
WC
Popescu
Delia L
DL
Tiago de Oliveira
Filipe
F
Wang
Dong
D
Que
Lawrence
L
Collins
Terrence J
TJ
Münck
Eckard
E
Bominaar
Emile L
EL
D000577:Amides / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D007536:Isomerism; D047029:Lactams, Macrocyclic / Q000737:chemistry*; D008280:Magnetics; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000737:chemistry*; D012996:Solutions; D015204:Spectroscopy, Mossbauer; D014867:Water / Q000737:chemistry
D000577:Amides; D047029:Lactams, Macrocyclic; D009942:Organometallic Compounds; D012996:Solutions; D014867:Water; D007501:Iron