Oscillatory Briggs-Rauscher reactions involving macrocyclic transition-metal complexes

New forms have been observed for oscillatory Briggs-Rauscher reactions catalyzed by macrocyclic nickel complexes. The number of oscillations in the reaction increases in the presence of cobalt complexes. Suggestions are made on how the catalysts act in these systems.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 30, No. 3, pp. 167–171, May–June, 1994.     

Chromatographic study of anionic complexes

Summary The diffusion of tartrate complexes of Cu²⁺, Co²⁺, Ni²⁺ and Cd²⁺ through filter paper strips has been examined using 50% and 60% ethanol as solvents. The R_f values are higher when 50% ethanol is used. When 50% ethanol is used, it is noted in the case of Cu²⁺, Co²⁺ and Ni²⁺ that the R_f values decrease with the addition of tartrate in the beginning. Then the value increases and finally becomes constant. In case of Cd²⁺ the R_f value decreases by the addition of tartrate. In 60% ethanol the R_f value does not change by small additions of tartrate but decreases with higher concentration of the complexing agent. In case of Cd²⁺ the R_f value becomes zero by increasing the concentration of tartrate.Part I: See Z. analyt. Chem. 159, 332 (1957/58).     

One-electron redox reactions of trifluoperazine in aqueous solutions

Absolute rate constants have been measured for the reactions of the primary and specific one-electron oxidant radicals with the protonated form of trifluoperazine (TFP). The primary radicals, e^- _aq and OH·, react with TFP at diffusion controlled rates. The transients thus produced have been characterized. Halogenated aliphatic peroxyl radicals oxidize TFP with rate constants between 10⁷ and 10⁸ dm³ mol^-1 s^-1, depending on the structure of the peroxyl radical. The reactivity of peroxyl radicals has been found to vary with Taft's inductive parameter. Oxidation of TFP at acidic pH has been studied using stopped-flow technique. The reaction between TFP radical cation and ascorbic acid has also been examined using pulse radiolysis technique. The results indicate that TFP radical cation is repaired by ascorbate. One-electron reduction potential of TFP · + /TFP at pH 3.5 has been calculated to be 0.964 V vs. NHE.     

One-electron redox reactions of troxerutin in aqueous solutions

The oxidation of flavonoids is of great interest because of their action as antioxidants with the ability to scavenge radicals by means of electron-transfer processes. The redox reactions of the flavonoid derivative troxerutin, (2-[3,4-bis-(2-hydroxyethoxy) phenyl]-3[[6-deoxy-α-L-manno-pyranosyl)-β-(D-glucopyranosyl]-oxy]-5-hydroxy-7-(2-hydroxyethoxy)-4H-1-benzo-pyran-4-one), were investigated over a wide range of conditions, using pulse radiolysis and cyclic voltammetry. The oxidation mechanism proceeds in sequential steps. One-electron redox potentials for troxerutin were found to be +1.196, +0.846 and −0.634 V vs. NHE.     

Chromatographic study of anionic complexes

Summary In this paper we have reported our results on the attempted separation of copper(II), nickel(II), cobalt(II) and iron(III) in mixtures by filter paper strip chromatography, using aqueous ethanol as solvent. The effect of the presence of varying concentrations of citrate ion as a complexing agent in the mixtures has been studied. The complexing agent has been added in the metal solution, and not in the solvent as usually done by previous workers.     

Chromatographic study of anionic complexes

Summary In this paper the variation of diffusion, through filter paper strips by the ascending method, of citrate complexes of Cu²⁺, Ni²⁺, Co²⁺ and Fe³⁺ has been studied using 50%, 55% and 60% ethanol as solvents. The R_f value is found to be less with higher concentrations of ethanol used. It has been noted that with 50% ethanol the R_f value increases with the addition of citrate and finally tends to become constant with high concentrations of citrate ions. In 55% ethanol the R_f value becomes constant at a later stage. In 60% ethanol it is noted that the R_f value does not change with small additions of citrate, but on increasing its concentration the R_f value begins to diminish.Part II see Z. analyt. Chem. 165, 81 (1959).     

Chromatographic study of anionic complexes

Summary In this paper the variation of diffusion, through a filter paper strip by the ascending method, of cuprioxalate complex has been studied. Various mixtures of Cu+^2üC₂O ₄ ^2– ions have been investigated. It has been noted that till there is a precipitation, the R_f values tend to decrease and finally reach nearly to zero, when the oxalate precipitates completely. With redissolution of the precipitate to form the complex anion, R_f values increase again to a maximum and then have a slight tendency to diminish. No tailing occurs in the chromatograms in cases where the copper has passed into the anion.     

Terminal, anionic carbide, nitride, and phosphide transition-metal complexes as synthetic entries to low-coordinate phosphorus derivatives

Anionic terminal one-atom nitride, phosphide, and carbide complexes are excellent starting materials for the synthesis of ligands containing low-coordinate phosphorus centers in the protecting coordination sphere of the metal complex. Salt-elimination reactions with chlorophosphanes lead to phosphaisocyanide, iminophosphinimide, and diorganophosphanylphosphinidene complexes in which the unusual phosphorus ligands are stabilized by coordination. X-ray structure analyses and density-functional calculations illuminate the bonding in these compounds.     

Density functional theory based molecular-dynamics study of aqueous iodide solvation

We study the solvation of iodide in water using density functional theory based molecular-dynamics simulations. Detailed analysis of the structural and dynamical properties of the first solvation shell is presented, showing a disruptive influence of the ion on the local water structure. Iodide-water hydrogen bonding is weak, compared to water-water hydrogen bonds. This effective repulsive ion-water interaction leads to the formation of a quite unstructured solvation shell. The dynamics of water molecules surrounding the iodide is relatively fast. The intramolecular structural and electronical properties of water molecules around the ion are not affected.     

Density functional theory based molecular-dynamics study of aqueous fluoride solvation

We use density functional theory based molecular-dynamics simulations to study the aqueous solvation of the fluoride anion. Our studies are focused on the first solvation shell and have resulted in detailed information on its structural and dynamical properties. The fluoride ion leads to the formation of a rigid solvation shell, qualitatively consistent with simulation and experimental studies, classifying fluoride as a "structure making" particle. However, quantitatively we find the solvation shell to be less structured and more mobile than predicted from empirical force-field simulation. The influence on the intramolecular electronical and structural properties of water is minimal, as observed for other halogens. We propose two distinct mechanisms for the exchange of bulk and first solvation shell water molecules.     

Density-functional study of two Fe4-based single-molecule magnets

We present the results of our all-electron density-functional calculations on the electronic structure and magnetic anisotropy energy of the [Fe4(OMe)6(dpm)6] and [Fe4(thme)2(dpm)6] molecular clusters, which are experimentally found to behave as single-molecule magnets. The calculated magnetic anisotropy energy barriers are 2.65 and 15.8 K, respectively, which agree with the experimental data. We also present a density-functional study on the effect of the structure distortions on the magnetic anisotropy of the [Fe(H2O)6]3+ complex. This study, together with an analysis of the projected anisotropies of each iron ion in both molecular clusters, allows us to qualitatively understand why the magnetic anisotropy energy (MAE) barrier of the second single-molecule magnet (SMM) is larger than the MAE of the first SMM.     

Density-functional theory study of Iron(III) hydrolysis in aqueous solution

Fe(III) hydrolysis in aqueous solution has been investigated using density-functional methods (DFT). All possible structures arising from different tautomers and multiplicities have been calculated. The solvation energy has been estimated using the UAHF-PCM method. The hydrolysis free energies have been estimated and compared with the available experimental data. The different hydrolysis species have distinct geometries and electronic structures. We have shown that improvement of theory level in calculating the electronic energy does not necessarily improve the estimated free energies in aqueous solution since the UAHF-PCM is a simple method that neglects specific interactions with the solvent. Therefore, it is important to have the correct balance between theory level used in the electronic calculation and the UAHF-PCM. The PBE/TZVP/UAHF-PCM method has been found to describe correctly the hydrolysis energies of Fe(III), deviating about 3.0 kcal mol(-1) from experimental values.     

A thermodynamic study of two anionic amphiphilic penicillins in aqueous solution by ultrasound speed measurements

The critical concentrations of sodium cloxacillin and sodium dicloxacillin penicillins in aqueous solution were determined over the temperature range 288.15–313.15 K by a method based on deconvolution into Gaussians of the second derivative of the measured ultrasound velocity. The mass action model was used to calculate the thermodynamic standard quantities: free Gibbs energy, enthalpy and entropy of aggregate formation. The results are discussed in terms of the structure of the drug aggregates.     

Pulse radiolysis study of redox reactions of safranine T in aqueous solutions: One electron oxidation

One electron oxidation of safranine T by specific oxidizing radicals such as Cl^-₂, Tl²⁺, Tl(OH)⁺, N^.₃, Br^-₂ etc. has been studied using the nanosecond pulse radiolysis technique. Reaction of free Br^. atom has also been investigated at neutral pH. The semioxidized safranine species formed by these reactions have been shown to exist in two conjugate acid-base forms with pK_a=4.0. Their spectral and kinetic parameters have been evaluated. Using N^.₃/N^-₃ and I^-₂/2I^- as reference couples, the one electron reduction potential of the semioxidized safranine has been determined to be 1.13±0.02 V vs NHE. The absorption spectra, second order decay rate constant and the pK_a of the OH-reaction product revealed features quite different from that of the semioxidized species suggesting that the mode of OH reaction is not via electron abstraction.     

Thermal stability of transition-metal complexes

This review aims at justifying the relationship between the room-temperature structures of transition-metal complexes and their thermal stabilities. The different factors affecting the thermal stability were also clarified. The survey of a larger number of transition-metal complexes showed various correlations of thermal stability with metal ion, ligand character or counterion.     

Pyridine-type complexes of transition-metal halides

Manganese(II) chloride complexes with 3,4- and 3,5-lutidine have been prepared. The crystal symmetry and cell dimensions have been calculated on the basis of powder diffraction data. The compounds were characterised also by FT-IR spectrometry. The thermal decomposition of the complexes has been studied by thermogravimetry and DSC. By plotting densities vs. molar mass, the diagram obtained has correspondence to similar observations in other solid metal-lutidine complex systems. This revised version was published online in August 2006 with corrections to the Cover Date.     

Solid-phase synthesis of transition-metal complexes

This overview highlights recent progress in the field of selective construction of linear, oligonuclear transition-metal complexes by using solid-phase synthesis procedures. Two general protocols have been identified: formation of coordinative bonds between metal centres and bridging ligands and formation of covalent bonds between preformed kinetically inert transition-metal-containing building blocks in the chain growth step. Currently available suitable building blocks for the second approach are based on ferrocene units, bis(terpyridine)-ruthenium(II) moieties or metal porphyrins.     

Generation of OH radicals in redox reactions of cobalt corrin complexes

Corrin complexes of cobalt reduce molecular oxygen to H₂O₂ in the presence of a reducing agent (ascorbic acid or ubiquinol Q₉H₂). The complex of divalent cobalt [Co^II(cor)]_OMe ⁺ClO₄ ^– breaks down H₂O₂ according to a radical mechanism, with the formation of OH radicals.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2679–2683, December, 1989.     

Ligand redox activity and mixed valency in first-row transition-metal complexes containing tetrachlorocatecholate and radical tetrachlorosemiquinonate ligands

Ligand noninnocence occurs for complexes composed of redox-active ligands and metals, with frontier orbitals of similar energy. Usually methods of analysis can be used to define the charge distribution, and cases where the metal oxidation state and ligand charge are unclear are unusual. Ligands derived from o-benzoquinones can bond with metals as radical semiquinonates (SQ(?-)) or as catecholates (Cat(2-)). Spectroscopic, magnetic, and structural properties can be used to assess the metal and ligand charges. With the redox activity at both the metal and ligands, reversible multicomponent redox series can be observed using electrochemical methods. Steps in the series may occur at either the ligand or metal, and ligand substituent effects can be used to tune the range of ligand-based redox steps. Complexes that appear as intermediates in a ligand-based redox series may contain both SQ and Cat ligands "bridged" by the metal as mixed-valence complexes. Properties reflect the strength of metal-mediated interligand electronic coupling in the same way that ligand-bridged bimetallics conform to the Robin and Day classification scheme. In this review, we will focus specifically on complexes of first-row transition-metal ions coordinated with three ligands derived from tetrachloro-1,2-benzoquinone (Cl(4)BQ). The redox activity of this ligand overlaps with the potentials of common metal oxidation states, providing examples of metal- and ligand-based redox activity, in some cases, within a single redox series. The strength of the interligand electronic coupling is important in defining the separation between ligand-based couples of a redox series. The complex of ferric iron will be described as an example where coupling is weak, and the steps associated with the Fe(III)(Cl(4)SQ)(3)/[Fe(III)(Cl(4)Cat)(3)](3-) redox series are observed over a narrow range in electrochemical potential.