- Spectroscopic Evidence of Pore Geometry Effect on Axial Coordination of Guest Molecules in Metalloporphyrin-Based Metal Organic Frameworks
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A systematic comparison of host-guest interactions in two iron porphyrin-based metal-organic frameworks (MOFs), FeCl-PCN222 and FeCl-PCN224, with drastically different pore sizes and geometries is reported in this fundamental spectroscopy study. Guest molecules (acetone, imidazole, and piperidine) of different sizes, axial binding strengths, and reactivity with the iron porphyrin centers are employed to demonstrate the range of possible interactions that occur at the porphyrin sites inside the pores of the MOF. Binding patterns of these guest species under the constraints of the pore geometries in the two frameworks are established using multiple spectroscopy methods, including UV-vis diffuse reflectance, Raman, X-ray absorption, and X-ray emission spectroscopy. Line shape analysis applied to the latter method provides quantitative information on axial ligation through its spin state sensitivity. The observed coordination behaviors derived from the spectroscopic analyses of the two MOF systems are compared to those predicted using space-filling models and relevant iron porphyrin molecular analogues. While the space-filling models show the ideal axial coordination behavior associated with these systems, the spectroscopic results provide powerful insight into the actual binding interactions that occur in practice. Evidence for potential side reactions occurring within the pores that may be responsible for the observed deviation from model coordination behavior in one of the MOF/guest molecule combinations is presented and discussed in the context of literature precedent.
- Kucheryavy, Pavel,Lahanas, Nicole,Lockard, Jenny V.
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- Photochemistry of Nitrosyl Porphyrins in the Temperature Range 180-300 K and the Effects of Pyridine on Photodenitrosylation of Nitrosyliron Tetraphenylporphyrin
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Nitrosylmetal tetraphenylporphyrin (NOMTPP, M=Fe,Co, and Mn) in benzene solutions undergoes facile photodenitrosylation to give NO and metal(II) tetraphenylporphyrin, MIITPP.The photodenitrosylation yields of NOFeTPP and NOCoTPP are respectively determined as 0.50 +/- 0.05 and 1.0 +/- 0.05 at both excitation wavelengths 355 and 532 nm.The yield, Φ, in toluene is expressed as a function of temperature: Φ = (1 + 1.56 x 10-2 exp(2400/RT))-1 for NOFeTPP and Φ = (1 + 1.02 x 10-6 exp(5200/RT))-1 for NOCoTPP.Contrary to NOFeTPP and NOCoTPP, the photodenitrosylation yields, Φ, of NOMnTPP are independent of temperature in the range 300-180 K and exhibit excitation wavelength dependence: Φ = 0.78 +/- 0.05 at 355 nm and Φ + 0.62 +/- 0.05 at 532 nm.The effects of the central metal on photodenitrosylation are described.The laser photolysis of NOFeTPP in the presence of low concentration of pyridine revealed that the FeIITPP initially produced reacts with a pyridine molecule, Py, to form five-coordinate (Py)FeIITPP.The five-coordinate (Py)Fe%II%TPP further reacts with Py to give six-coordinate (Py)2FeIITPP, which recombines with NO to regenerate NOFeTPP.The kinetic study has demonstrated that the five-coordinate (Py)FeIITPP which is in equilibrium with (Py)2FeIITPP is responsible for the recombination reaction of (Py)2FeIITPP and NO.
- Hoshino, Mikio,Kogure, Mieko
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p. 5478 - 5484
(2007/10/02)
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- Electron density studies of porphyrins and phthalocyanines. 7. Electronic ground state of bis(pyridine)(meso-tetraphenylporphinato)iron(II)
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The structure and electron density distribution of bis(pyridine)(meso-tetraphenylporphinato)iron(II), FeN6C54H38, have been determined by using two sets of X-ray diffraction data collected at 110-120 K. Crystal data: Mr = 826.79, triclinic, P1, Z = 1, a = 9.423 (1) ?, b = 10.560 (2) ?, c = 11.998 (2) ?, α = 101.70 (1)°, β = 104.96 (1)°, γ = 111.95 (2)°, V = 1008.50 (2) ?3, dcalcd = 1.361 g/cm3, μ = 4.17 cm-1, λ(Mo Kα) = 0.71073 ?. R factors of the final aspherical atom refinements: R = 2.44%, Rw = 2.41% for data set 1 [(sin θ)/λmax = 0.91 ?-1]; R = 3.98%, Rw = 2.85% for data set 2 [(sin θ)/λmax = 1.15 ?-1]. The Fe-N(pyridine) distance is 2.037 (2) ?, while the average Fe-N(porphinato) distance is 2.001 (1) ?. Bond lengths and electron density distribution indicate that the iron atom is in the low-spin state. The experimental populations of the iron d orbitals are close to those from an extended Hückel calculation, with significant population of the crystal field destabilized orbitals, indicating σ-donation from the coordinated ligands. Covalency parameters derived from the dx2-y2 populations in three complexes correlate with bond lengths. π-Back-bonding is suggested by the less-than-six total electron population of the dxz, dyz, and dxy orbitals. The calculated M?ssbauer shift is equal within experimental error to the spectroscopically observed value and has a negative sign.
- Li, Naiyin,Coppens, Philip,Landrum, John
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p. 482 - 488
(2008/10/08)
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- Biomimetic oxidation with molecular oxygen. Selective carbon-carbon bond cleavage of 1,2-diols by molecular oxygen and dihydropyridine in the presence of iron-porphyrin catalysts
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The selective carbon-carbon bond cleavage of 1,2-diols in the presence of an iron-porphyrin complex, molecular oxygen, and 1-benzyl-3-carbamoyl-1,4-dihydropyridine is reported. The C-C bonds of aryl-substituted ethane-1,2-diols were cleaved exclusively to aldehydes or ketones as the oxidation products at room temperature. The reaction rates were influenced by the steric hindrance of the substituents both in the catalysts and diols, but no differences in the reactivities were observed between the two stereo isomers (meso and dl) of diols. A kinetic analysis of this bond cleavage reaction is consistent with the reaction mechanism consisting of the initial binding of diol on the active catalyst forming an intermediate complex and its subsequent breakdown in the rate-determining step of the catalytic cycle. The initial binding step is favorable for electron-deficient diols and is influenced by steric hindrance, whereas the rate-determining bond cleavage step is accelerated by electron-rich diols and unaffected by the steric effect. The mechanism of this diol cleavage reaction is discussed on the basis of these observations. The selective carbon-carbon bond cleavage of 1,2-diols in the presence of an iron-porphyrin complex, molecular oxygen, and 1-benzyl-3-carbamoyl-1,4-dihydropyridine is reported. The C-C bonds of aryl-substituted ethane-1,2-diols were cleaved exclusively to aldehydes or ketones as the oxidation products at room temperature. The reaction rates were influenced by the steric hindrance of the substituents both in the catalysts and diols, but no differences in the reactivities were observed between the two stereo isomers (meso and dl) of diols. A kinetic analysis of this bond cleavage reaction is consistent with the reaction mechanism consisting of the initial binding of diol on the active catalyst forming an intermediate complex and its subsequent breakdown in the rate-determining step of the catalytic cycle.
- Okamoto,Sasaki,Oka
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p. 1187 - 1196
(2007/10/02)
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- Dioxygen Activation in the Photochemistry of some Oxo-metalloporphyrin Complexes
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Ultraviolet irradiation of the peroxo-complexes and (tpp = 5,10,15,20-tetraphenylporphyrinate) induces elimination of O2 and generation of the corresponding oxometalloporphyrins and .Reductive elimination o
- Bergamini, Paola,Sostero, Silvana,Traverso, Orazio,Deplano, Paola,Wilson, Lon J.
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p. 2311 - 2314
(2007/10/02)
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- NITROSOALKANE COMPLEXES OF IRON-PORPHYRINS: ANALOGY BETWEEN THE BONDING PROPERTIES OF NITROSOALKANES AND DIOXYGEN.
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The present paper describes different preparations of iron-porphyrin-nitrosoalka complexes and their study by various spectroscopic methods including an X-ray analysis. This study definitely proves the existence of the Fe**I**I-RNO bond, establishes the end-on N-binding mode of nitrosoalkanes in these ferroporphyrin complexes and gives information on the electronic structure of the Fe-RNO bond. Moreover, it points out a striking similarity between the bonding properties of nitrosoalkanes and dioxygen as ligands of iron(II)-porphyrins. Refs.
- Mansuy,Battioni,Chottard,Riche,Chiaroni
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p. 455 - 463
(2007/10/02)
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- New Five- and Six-Coordinate Imidazole and Imidazolate Complexes of Ferric Tetraphenylporphyrine
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The synthesis of several new imidazole and imidazolate complexes of ferric tetraphenylporphyrine (TPP) are reported.The following coplexes have been made with L = imidazole (ImH) or 4-methylimidazole (4MeImH) and L- = imidazolate (Im-) or 4-methylimidazolate (4MeIm-): FeTPP(L)(L-), -2>-, and (SbF6).Addition of Im- to FeTPPCl resulted in the formation first of the imidazolate-bridged complex + and then of -.Similar addition of 4MeIm- to FeTPPCl resulted in the formation first of the high-spin mononuclear complex FeTPP(4MeIm) and then of -.The affinity of (SbF6) for a second 4MeImH was found to be very high, with K >/= 107 M-1 in toluene, 25 deg C.By contrast, 4MeImH was found preferentially to hydrogen bond to Fe(TPP)(4MeIm), with K ca. 5 * 104 M-1 in THF, 25 deg C.Coordination of 4MeImH was only observed at high concentration of ligand (K ca. 50 +/- 10 M-1).The monoimidazole complex (SbF6) was concluded to be high spin after a comparison of the visible spectral properties of a large number of ferric TPP complexes.
- Quinn, Robert,Nappa, Mario,Valentine, Joan S.
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p. 2588 - 2595
(2007/10/02)
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- A new route to thiocarbonyl-iron complexes: Preparation of FeII[porphyrin][C(Cl)SR] carbene complexes and their conversion to FeII[porphyrin][CS] complexes
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The reaction of trichloromethyl-thioalkyl compounds including the widely used fungicides Captan and Folpet with iron(II) porphyrins in the presence of a reducing agent in excess leads to the formation of new carbene complexes, Fe[porphyrin][C(Cl)SR], whose stabilities are strongly dependent on the nature of the R substituent. Upon treatment by a catalytic amount of FeCl2 or CuCl2, some of them are decomposed into thiocarbonyliron(II)-porphyrin complexes, Fe[porphyrin][CS], in nearly quantitative yields. Various Fe[porphyrin][CS][L] complexes have thus been obtained by this method and characterized by UV-visible, IR, and 1H and 13C NMR spectroscopy. They are very stable to dioxygen and nucleophiles but react with primary amines R′NH2 in excess to give the Fe[porphyrin][CNR′][R′NH2] complexes. Reduction of C6H5SCHCl2 by iron(II) tetraphenylporphyrin, Fe[TPP], leads to the Fe[TPP][CHSC6H5] complex, which is the first example of an iron(II) porphyrin complex bearing a secondary CHR carbene.
- Battioni, Jean-Paul,Chottard, Jean-Claude,Mansuy, Daniel
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p. 2056 - 2062
(2008/10/08)
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