Two-Step Spin-Transition Iron(III) Compound with a Wide [High Spin-Low Spin] Plateau

A new iron(III) coordination compound exhibiting a two-step spin-transition behavior with a remarkably wide [HS-LS] plateau of about 45 K has been synthesized from a hydrazino Schiff-base ligand with an N,N,O donor set, namely 2-methoxy-6-(pyridine-2-ylhydrazonomethyl) phenol (Hmph). The single-crystal X-ray structure of the coordination compound {[Fe(mph)(2)](ClO4)(MeOH)(0.5)(H2O)(0.5)}(2) (1) determined at 150 K reveals the presence of two slightly different iron(III) centers in pseudo-octahedral environments generated by two deprotonated tridentate mph ligands. The presence of hydrogen bonding interactions, instigated by the well-designed ligand, may justify the occurrence of the abrupt transitions. 1 has been characterized by temperature-dependent magnetic susceptibility measurements, EPR spectroscopy, differential scanning calorimetry, and Fe-51 Mossbauer spectroscopy, which all confirm the occurrence of a two-step transition. In addition, the iron(III) species in the high-spin state has been trapped and characterized by rapid cooling EPR studies.

Solvent effects on spectrophotometric titrations and vibrational spectroscopy of 5,10,15-triphenyl-20-(4-hydroxyphenyl)porphyrin in aqueoius DMF

The spectrophotometric titration by sodium hydroxide of 5,10,15-triphenyl-20-(4-hydroxyphenyl)porphyrin ((OH)(1)PH2) is studied as a function of solvent composition of DMF-H2O binary solvent mixture ([OH-] = 0.04 M). Combining the structure changes of the porphyrin and the "four orbital" model of Gouterman, many features of the optical spectra of this deprotonated para-hydroxy-substituted tetraphenylporphyrin in different composition of binary solvent mixtures can be rationalized. In highly aqueous solvents, the changes of the titration curves are shown to be mainly due to hydrogen-bonding of the oxygen of the phenoxide anion group by the hydroxylic solvent, Which decreases the energy of the phenoxide anion pi orbital. Thus the phenoxide anion pi orbital cannot cross over the porphyrin Tr orbital being a different HOMO. However, its energy is close to that of the porphyrin pi orbitals. As a result, in the visible region, no charge-transfer band is observed, while in the visible-near region, the Soret peak split into two components. In nonaqueous solvents, the changes are mainly attributed to further deprotonation of pyrrolic-Hs of (OH) 1PH2 by NaOH and coordination with two sodium ions to form the sodium complex of (OH) 1PH2, which turns hyperporphyrin spectra of deprotonated of phenolic-H of (OH)(1)PH2 into three-banded spectra of regular metalloporphyrin.

Electrocatalytic reduction of oxygen at multi-walled carbon nanotubes and cobalt porphyrin modified glassy carbon electrode

The multi-walled carbon nanotubes (MWNTs) modified glassy carbon electrode exhibited electrocatalytic activity to the reduction of oxygen in 0.1 M HAc-NaAc (pH 3.8) buffer solution. Further modification with cobalt porphyrin film on the MWNTs by adsorption, the resulted modified electrode showed more efficient catalytic activity to O-2 reduction. The reduction peak potential of O-2 is shifted much more positively to 0.12 V (vs. Ag/AgCl), and the peak current is increased greatly. Cyclic voltammetry (CV), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), were used to characterize the material and the modified film on electrode surface. Electrochemical experiments gave the total number of electron transfer for oxygen reduction as about 3, which indicated a co-exist process of 2 electrons and 4 electrons for reduction of oxygen at this modified electrode. Meanwhile, the catalytic activities of the multilayer film (MVVNTs/CoTMPyP)(n) prepared by layer-by-layer method were investigated, and the results showed that the peak current of O-2 reduction increased and the peak potential shifted to a positive direction with the increase of layer numbers.

Bis[tris(2,2 '-bipyridyl-kappa N-2,N ')iron(II)] cyclo-tetravanadate decahydrate

The hydrothermal reactions of metavanadate and divalent iron salts in the presence of nitrogen-donor chelating ligands yield the complex [Fe(C10H8N2)(3)](2)[V4O12].10H(2)O, which consists of one centrosymmetric eight-membered ring [V4O12](4-) anion cluster, formed by four VO4 tetrahedra sharing vertices, two discrete octahedral [Fe(C10H8N2)(3)](2+) cations, formed by three 2,2'-bipyridyl ligands coordinated to Fe-II, and ten water molecules of solvation. The anion and coordination cations are isolated and form anion and cation layers, respectively. In the anion layers, these anions and water molecules of solvation are linked to each other, in a two-dimensional motif, through hydrogen-bonding interactions.

Polymerization of methyl methacrylate by iron(II) pyridinebisimine complexes

Fe(II) pyridinebisimine complexes activated with trialkylaluminium or modified methylaluminoxane (MMAO) as catalysts were employed for the polymerization of methyl methacrylate. Polymer yields, activities and polymer molecular weights as well as molecular weight distributions can be controlled over a wide range by the variation of the structures of the Fe(II) pyridinebisimine complexes and the reaction parameters such as Al/Fe molar ratio, monomer/catalyst molar ratio, monomer concentration, reaction temperature and time applied to the polymerization of methyl methacrylate. Under optimum condition, the catalytic activity of Fe(II) complex is of up to 74.5 kg(polym)/mol(Fe)h.

The synthesis and catalytic activity of poly(bis(imino)pyridyl) iron(II) metallodendrimer

The first and second generation carbosilane dendrimers with silicon hydride terminated were synthesized, and then reacted with bis(imino)pyridyl containing allyl [4-CH2==CHCH2-2,6-(Pr2C6H3N)-Pr-i==CMe(C5H3N)MeC==N(2,6-'Pr2C6H3)], in the presence of H2PtCl6 as a hydrosilylation catalyst, to afford the first and second generation carbosilane supported ligands. Complexation reactions with FeCl(2)(.)4H(2)O give rise to iron-containing carbosilane dendrimers with FeCl2 moieties bound on the periphery. The metallodendrimers were used as catalyst precursors, activated with modified methylaluminoxane, for the polymerization of ethylene. In the case of low Al/Fe molar ratio, the metallodendrimers display much higher catalytic activity towards ethylene polymerization and produce much higher molecule weight polyethylenes than the corresponding single-nuclear complex under the same conditions.

Extraction and separation of cadmium(II), iron(III), zinc(II), and europium(III) by Cyanex302 solutions using hollow fiber membrane modules

The mass transfer behaviors of Cd(II), Fe(III), Zn(II), and Eu(III) in sulfuric acid solution using microporous hollow fiber membrane (HFM) containing bis(2,4,4-trimethylpentyl)monothiophosphinic acid (commercial name Cyanex302) were investigated in this paper. The experimental results showed that the values of the mass transfer coefficients (K-w) decreased with an increase of H+ concentration and increased with an increase of extractant Cyanex302 concentration. The mass transfer resistance of Eu3+ was the largest because K-w value of Eu3+ was the smallest. The order of mass transfer rate of metal ions at low pH was Cd > Zn > Fe > Eu. Mixtures of Zn2+ and Eu3+ or of Zn2+ and Cd2+ were well separated in a counter-current circulation experiment using two modules connected in series at different initial acidity and concentration ratio. These results indicate that a hollow fiber membrane extractor is capable of separating the mixture compounds by controlling the acidity of the aqueous solution and by exploiting different mass transfer kinetics. The interfacial activity of Cyanex302 in sulfuric acid solution was measured and interfacial parameters were obtained according to Gibbs adsorption equation.

Micron-granula polyolefin with self-immobilized nickel and iron diimine catalysts bearing one or two allyl groups

Self-immobilized nickel and iron diimine catalysts bearing one or two allyl groups of [ArN=C](2)(C10H6)NiBr2 [Ar = 4-allyl-2,6-(i-Pr)(2)C6H2] (1), [ArN=C(Me)[Ar'N=C(Me)]C5H3NFeCl2 [Ar = Ar' = 4-allyl-2,6-(i-Pr)(2)C6H3, Ar = 2,6-(i-Pr)(2)C6H3, and Ar' = 4-allyl-2,6-(i-Pr)(2)C6H3] were synthesized and characterized. All three catalysts were investigated for olefin polymerization. As a result, these catalysts not only showed high activities as the catalyst free from the allyl group, such as [ArN=C](2)C10H6,NiBr2 (Ar = 2,6-(i-Pr)(2)C6H2)], but also greatly improved the morphology of polymer particles to afford micron-granula polyolefin. The self-immobilization of catalysts, the formation mechanism of microspherical. polymer, and the influence on the size of the particles are discussed. The molecular structure of self-immobilized nickel catalyst 1 was also characterized by crystallographic analysis.

Sequential deprotonation of meso-(p-hydroxyphenyl)porphyrins in DMF: From hyperporphyrins to sodium porphyrin complexes

Sequential deprotonations of meso-(p-hydroxyphenyl)porphyrins (p-OHTPPH2) in DMF + H2O (V/V = 1:1) mixture have been verified to result in the appearance of hyperporphyrin spectra. However, when the deprotonations of these p-OHTPPH2 are carried out in DMF, the spectral changes differ considerably from those in the mixture mentioned above. At low [OH-], the optical spectra in the visible region are still considered to have characteristics of hyperporphyrin spectra. Further deprotonation at much higher basicity makes the optical spectra form three-banded spectra similar to those in the acidic solution. To clarify the molecular origins of these changes, UV-vis, resonance Raman (RR), proton nuclear magnetic resonance (H-1 NMR) experiments are carried out. Our data give evidence that p-OHTPPH2 in DMF can be further deprotonated of pyrrolic-H by higher concentrated NaOH, due to an aprotic medium like DMF effectively weakening the basicity of the porphyrin relative to that of the NaOH, and coordinates with two sodium ions (except the sodium ions that interact with the peripherial phenoxide anions) to form the sodium complexes of p-OHTPPH2 (Na2P, to lay a strong emphasis on the sodium ions that coordinate with the central nitrogen atom), which can be regarded as the porphyrin anions being perturbed by the sodium cations due to their highly ionic character.

Studies of interaction between iron (III) and intermediates of synthetic neuromelanin by means of cyclic voltammetry of Fe(CN)(3-)(6) and dopamine

Neuromelanin is a complex polymer pigment found primarily in the dopaminergic neurons of the human substantia nigra, whose composition is complex including production of dopamine auto-oxidation, glutathione and a variety of amino acid. Neuromelanin forms stable complex with iron (111). We observed that 5,6-dihydroxyindole and its ramification possessed strong ability of chelating iron (111), and they are the production of dopamine auto-oxidation under physiological pH condition. In the present Of L-Cysteine, the relative yields of electrochemical oxidation of dopamine also had strong ability of chelating iron (111). The experimental results suggest that 5,6-dihydroxyindole and 5-S-cysteineldopamine play important roles in the process of synthetic neuromelanin chelating iron (111).

Substitution effect of nitrogen atoms with carbon atoms in porphyrin on the electronic structure and excited states properties

Density functional theory (DFT) electronic structure calculations were carried out to predict the structures and the absorption and emission spectra for porphyrin and a series of carbaporphyrins-carbaporphyrin, adj-dicarbaporphyrin, opp-dicarbaporphyrin, tricarbaporphyrin and tetracarbaporphyrin. The ground- and excited-state geometries were optimized at the B3LYP/6-31g(d) and CIS/6-31g(d) level, respectively. The optimized ground-state geometry and absorption spectra of porphyrin, calculated by DFT and time-dependent DFT (TDDFT), are comparable with the available experimental values. Based on the optimized excited-state geometries obtained by CIS/6-31g(d) method, the emission properties are calculated using TDDFT method at the B3LYP/6-31g(d) level. The effects of the substitution of nitrogen atoms with carbon atoms at the center positions of porphyrin are discussed. The results indicate that the two-pyrrole nitrogens are important to the chemical and physical properties for porphyrin.

Electron effect of p-substituent on iron(II) and cobalt(II) pyridinebisimine catalyst for ethylene polymerization

A series of 2,6-bis(imino)pyridyl iron and cobalt complexes bearing p-substituent [2,6-(ArN=CMe)(2)C5H3N]-MCl2 (Ar=2,6-Me2C6H3, 2,4,6-Me3C6H2, 2,6-Me-2-4-BrC6H2, 2,6-Me-2-4-ClC6H2, 2,4-Me-2-6-BrC6H2, 2,4-Me-(2)-6-ClC6H2, while M=Fe, Co) have been synthesized and investigated as catalysts for ethylene polymerization in the presence of modified methylaluminoxane as a cocatalyst. The electron effect and positions of the substitueni of pyridinebisimine ligands were observed to affect considerably catalyst activity and polymer property.

Synthesis, characterization and fabrication on a glassy carbon electrode of a tetra-iron substituted sandwich-type pentadecatungstodiarsenate heteropolyanion

A novel sandwich-type compound, Na-12[Fe-4(H2O)(2)(As2W15O56)2].41H(2)O, has been synthesized. The compound was well-characterized by means of IR, UV-vis, W-183 NMR and elemental analyses. The compound crystallizes in the triclinic, P (1) over bar symmetry group. The structure of the compound is similar to that of Na-16[M-4(H2O)(2)(As2W15O56)(2)].nH(2)O (M = Cu, Zn, Co, Ni, Mn, Cd), and consists of an oxo-aqua tetranuclear iron core, [(Fe4O14)-O-III(H2O)(2)], sandwiched by two trivacant alpha-Wells-Dawson structural moieties, alpha-[As2W15O56]. Redoxelectrochemistry of the compound has been studied in buffer solutions at pH = 4.7 using polarography and cyclic voltammetry ( CV). The compound exhibited four one-electron couples associated with the Fe(III) center followed by three four-electron redox processes attributed to the tungsten-oxo framework. The compound-containing monolayer and multilayer films have been fabricated on a 4-aminobenzoic acid modified glassy carbon electrode surface by alternating deposition with a quaternized poly(4-vinylpyridine) partially complexed with [Os(bpy)(2)Cl](2+/-). CV, X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy and atomic force microscopy (AFM) have been used to characterize the multilayer films.