25482-27-3Relevant articles and documents
Magnetic Transitions in Iron Porphyrin Halides by Inelastic Neutron Scattering and Ab Initio Studies of Zero-Field Splittings
Stavretis, Shelby E.,Atanasov, Mihail,Podlesnyak, Andrey A.,Hunter, Seth C.,Neese, Frank,Xue, Zi-Ling
, p. 9790 - 9801 (2015)
Zero-field splitting (ZFS) parameters of nondeuterated metalloporphyrins [Fe(TPP)X] (X = F, Br, I; H2TPP = tetraphenylporphyrin) have been directly determined by inelastic neutron scattering (INS). The ZFS values are D = 4.49(9) cm-1 for tetragonal polycrystalline [Fe(TPP)F], and D = 8.8(2) cm-1, E = 0.1(2) cm-1 and D = 13.4(6) cm-1, E = 0.3(6) cm-1 for monoclinic polycrystalline [Fe(TPP)Br] and [Fe(TPP)I], respectively. Along with our recent report of the ZFS value of D = 6.33(8) cm-1 for tetragonal polycrystalline [Fe(TPP)Cl], these data provide a rare, complete determination of ZFS parameters in a metalloporphyrin halide series. The electronic structure of [Fe(TPP)X] (X = F, Cl, Br, I) has been studied by multireference ab initio methods: the complete active space self-consistent field (CASSCF) and the N-electron valence perturbation theory (NEVPT2) with the aim of exploring the origin of the large and positive zero-field splitting D of the 6A1 ground state. D was calculated from wave functions of the electronic multiplets spanned by the d5 configuration of Fe(III) along with spin-orbit coupling accounted for by quasi degenerate perturbation theory. Results reproduce trends of D from inelastic neutron scattering data increasing in the order from F, Cl, Br, to I. A mapping of energy eigenvalues and eigenfunctions of the S = 3/2 excited states on ligand field theory was used to characterize the σ- and π-antibonding effects decreasing from F to I. This is in agreement with similar results deduced from ab initio calculations on CrX63- complexes and also with the spectrochemical series showing a decrease of the ligand field in the same directions. A correlation is found between the increase of D and decrease of the π- and σ-antibonding energies eλX (λ = σ, π) in the series from X = F to I. Analysis of this correlation using second-order perturbation theory expressions in terms of angular overlap parameters rationalizes the experimentally deduced trend. D parameters from CASSCF and NEVPT2 results have been calibrated against those from the INS data, yielding a predictive power of these approaches. Methods to improve the quantitative agreement between ab initio calculated and experimental D and spectroscopic transitions for high-spin Fe(III) complexes are proposed.
The oxidation of bromide ion by [(FeTPP)2O]+SbF6- In dichloromethanej
Hubbard, Colin D.,Jones, John G.,McKnight, John
, p. 3143 - 3148 (2007/10/03)
The oxidation of cetyltrimethylammonium bromide (CTAB) by mono-oxidised iron(m) tetraphenylporphyrin u-oxo-dimer, [(FeTPPOSbF, ; , has been found to be much slower than the corresponding oxidation of iodide ion, but can still be studied by stopped-flow techniques. The stoichiometry of the reaction has been established as 2 [Fe(TPP)2O]+ + 3Br -> 2(FeTPP)2O + Br3-. The rate law for the reaction is d [(FeTPP)2O]/df = [Fe(TPP)2O+] (kf [CTAB] -A'r). The rate constant for the first term has been identified with the rate determining forward process, the formation of the unstable Br2-, and the second term with the attack of Br2- on the uncharged u-oxo-dimer. A subsequent process involves what appears to be the rapid oxidation of Br2- in the presence of Br- to give Br3 . At 298 K kf is 737(±30) NT1 s-1 and k, is 0.80(±0.16) s-1. For kf, Δ = 58.8(±1.6) kJ mol-1, AS = 8.62(10.45) J K-1 moP1; for k, , ΔH = 43.6(110.8) kJ mol-1, AS = -97.8(136.0) J K-1 mol-1. The addition of cetyltrimethylammonium perchlorate (inert to reaction with the oxidised u-oxo-dimer) slowed the reaction in a manner which indicated competition between perchlorate and bromide for the formation of ion pairs with the oxidised iron(m) dimer, the bromide ion pair being the reactive one. The Royal Society of Chemistry 2000.
Studies of the chemical oxidation of iron(II) complexes of N-methylporphyrins to form the corresponding iron(III) complexes
Balch, Alan L.,La Mar, Gerd N.,Latos-Grazynski, Lechoslaw,Renner, Mark W.
, p. 2432 - 2436 (2008/10/08)
Oxidation of iron(II) N-methylporphyrin halide complexes with chlorine, bromine, or iodine in chloroform solution at -50°C produces the corresponding iron(III) N-methylporphyrin halide cations. The oxidations may be reversed by treating the product solutions with zinc. The iron(III) complexes have been characterized by electronic, 1H and 2H NMR, and ESR spectroscopy. The NMR results indicate that the Cs symmetry of the iron(II) parent complexes is retained upon oxidation. Characteristic 1H NMR shifts for these high-spin (S = 5/2) species include the very broad N-methyl resonance at ca. 270 ppm (observed only by 2H NMR), three pyrrole resonances in the 130-75 ppm region and one at ca. 2 ppm, pyrrole methylene resonances in the range 80-20 ppm and meso resonances at ca. -70 ppm. The electronic structure of these iron(III) complexes are similar to those of symmetrical high-spin, five-coordinate iron(III) porphyrins except for the local environment of the methylated pyrrole, which suffers from sharply reduced σ-spin transfer as a consequence of the longer Fe-N distance to that ring. On warming, these iron(III) complexes decompose by demetalation (for chloride complexes) or demethylation (for bromide complexes).
