1,720,966 research outputs found
The reaction of mu-oxo-bis(phthalocyaninato)iron(III) with hydrogen sulphide in the presence of pyridine. Evidence for axial coordination of dichloromethane
No full textThe oxo-bridged complex (py)FePc-O-FePc(py) (py = pyridine, Pc = phthalocyaninato dianion) reacts in dichloromethane with hydrogen sulphide giving elementary sulphur and the reduced (py)(2)(FePc) complex in the stoichiometric ratio 1:1. Under excess py and H,S, the reaction is first-order and the rate constant at a given py concentration is an increasing function of the reducing agent concentration, with asymptotic tendency to a limiting value. This latter depends on the pyridine concentration being higher the lower is the base concentration. When the reaction is carried out in pure pyridine, the rate constant is, instead, a strictly linear function of [H2S], with zero intercept. A reaction mechanism is proposed where the dichloromethane is directly involved in the axial coordination about the iron centers and H2S competes efficiently with both pyridine and solvent. Copyright (c) 2005 Society of Porphyrins & Phthalocyanines
The reaction of [bispyridinotetrakis(t-butyl)phthalocyaninato]iron(II) with dioxygen to give mu-oxo-bis[tetrakis(t-butyl)phthalocyaninato]iron(III)
No full textThe reaction of [bispyridinotetrakis(t-butl)phthalocyaninato]iron(II), (py)(2)FePc'. with dioxygen in CH2Cl2, gives almost quantitatively the oxo-bridged mu-oxo-bis[tetrakis(t-butyl)phthalocyaninato]iron(III) as the final, stable product. The reaction order with respect to the starting complex changes within a run. For t = 0. the rate is proportional to the ratio a(1) root y(0)/(a(2) + root y(0)) (Equation 1) where),, is the initial absorbance of the solution and a, and a, are linear functions of [O-2]. For t > 0, the instantaneous rate is instead described by the equation Rate = b [O-2] [A]/([A](0) - [A]) (Equation 2). where A is (py)(2)FePc' and the coefficient b is again proportional to [O-2]. A mechanism is proposed implying the presence of trace amounts of (py)(S)FePc' (S = axially bound CH2Cl2) in equilibrium with (py)(2)FePc'. Both species are able to generate the transient pentacoordinate (py)FePc' that may react with py and S, giving back the hexacoordinate precursors, or with dioxygen. giving ultimately the mu-oxo complex. At t = 0. the species (py)(S)FePc'. expected to be much more labile than (py),FePc'. is at its maximum concentration and is assumed to give the prevaling contribution to the instantaneous C rate. As the reaction proceeds, and free pyridine accumulates in the solution. the concentration of (py)(S)FePc' decreases rapidly and the transient (py) FePc' is produced essentially by the bispyridino complex. This fact and the still growing concentration of free pyridine account for the Equation 2. Finally, when the py concentration is buffered by addition of small amounts of base. the reaction attains a simple first order law. Present data further support the iron(III) formulation of the final mu-OXO product and are inconsistent with the iron(II) hypothesis put forward by some authors. Copyright (c) 2006 Society of Porphyrins & Phthalocyanines
Proprietà redox dei complessi a ponte di ossigeno mu-osso-bis(ftalocianinatoferro(III)) e mu-osso-bis(tetrakis(t-butil)ftalocianinatoferro(III))
No full textNuovi complessi di Pd(II) di tipo porfirazinico mono- e pentametallici come fotosensibilizzatori in soluzione di DMF per la produzione di ossigeno di singoletto 1O2
No full textComplessi mono e pentametallici di tipo porfirazinico come fotosensibilizzatori in campo farmaceutico
No full textDetermination of H(2)S solubility via the reaction with ferric hemoglobin I from the bivalve mollusc Lucina pectinata.
No full textTiO2- based photocatalysts in the decontamination of waters from organic pollutants
No full textPoster P3
Tetra-2,3-pyrazinoporphyrazines with Externally Appended Pyridine Rings. 4. UV−Visible Spectral and Electrochemical Evidence of the Remarkable Electron-Deficient Properties of the New Tetrakis-2,3-[5,6-di{2-(N-methyl)pyridiniumyl}pyrazino]porphyrazinatometal Octacations, [(2-Mepy)8TPyzPzM]8+ (M = MgII(H2O), CoII, CuII, ZnII)
No full textMetal derivatives of the octacationic tetrakis-2,3-[5,6-di{2-(N-methyl)pyridiniumyl}pyrazino]porphyrazine macrocycle [(2-Mepy)8TPyzPzH2]8+ (2-Mepy ) 2-(N-methyl)pyridiniumyl ring) isolated as water-soluble hydrated iodide salts of the general formula [(2-Mepy)8TPyzPzM](I8).xH2O, (M ) Mg(II)(H2O), Co(II), Cu(II), Zn(II); x = 2-5) were prepared from the corresponding neutral complexes [Py8TPyzPzM].xH2O previously reported. Reaction of these complexes with CH3I in N,N-dimethylformamide under mild conditions led to full quaternization of all eight pyridine N atoms and formation of the octacations [(2-Mepy)8TPyzPzM]8+. Clathrated water molecules could be eliminated from the species [(2-Mepy)8TPyzPzM](I8).xH2O by mild heating (< or = 100 °C) under vacuum, but the unsolvated species which were formed tended to rehydrate when exposed to air. Magnetic susceptibility measurements and EPR spectra prove that the Cu(II) and Co(II) complexes in the solid state are both paramagnetic with one unpaired electron, thus giving a low-spin state Co(II) for the latter compound. Studies of the charged species [(2-Mepy)8TPyzPzM]8+ in aqueous media at ca. 10-5 M concentration provide evidence for the occurrence of molecular aggregation, similar to what is seen for the related free-base species [(2-Mepy)8TPyzPzH2]8+ (see part 3 of this series, preceding paper in this issue), but the formation of monomeric species is generally favored upon dilution of the solutions. The same octacations are essentially monomeric in solutions of pyridine or dimethyl sulfoxide (DMSO), but traces of aggregation, if occasionally present, vanish with the time. Changes in the UV-visible spectra are observed in the Q- and B-band regions as a result of the quaternization at the pyridine N atoms. Cyclic voltammetry and thin-layer spectroelectrochemical data in DMSO show well-resolved reversible multistep one-electron reductions for both the unmethylated and methylated complexes, all of which appear to be ligand-centered, the only exception being reduction of the Co(II) complex. For this species, the first one-electron reduction is a metal-centered Co(II)- Co(I) process, but the site of electron transfer is reversed and the final product upon a further one-electron reduction is formulated as a CoII dianion as opposed to a Co(I) ?-anion radical. This sequence is similar to what was earlier reported for reduction of the same compound in pyridine. Reversible one-electron oxidations are also observed for the unmethylated species [Py8TPyzPzM].xH2O where M ) CoII and MnII in DMSO. Remarkably, the octacationic macrocycles [(2-Mepy)8TPyzPzM](I8).xH2O, (M ) Mg(II)(H2O), Co(II), Cu(II), and Zn(II); x = 2-5) are more easily reduced at any step of the reduction than the corresponding unquaternized species with the same metal ion. This indicates a higher tendency to stepwise electron uptake after the quaternization process, which enhances the charge redistribution capability within the species formed by the electroreduction
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
