Kinetic stability of complexes of some d-metals with 3,3′-bis(dipyrrolylmethene) in the binary proton-donor solvent acetic acid-benzene

The kinetics of dissociation of Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II) binuclear homoleptic double-stranded helicates with bis(2,4,7,8,9-pentametyldipyrrolylmethen-3-yl)methane (H₂L) of the [M₂L₂] composition in the binary proton-donor solvent acetic acid-benzene was studied. Protolytic dissociation of the helicates [M₂L₂] proceeds in accordance with the third order kinetic equation. Effect of the complexing metal nature is manifested in increased kinetic inertness in the following series of the helicates: [Cd₂L₂] < [Hg₂L₂] < [Cu₂L₂] < [Ni₂L₂] < [Zn₂L₂] < [Co₂L₂]. By the lability in similar environmental conditions the helicates [M₂L₂] are comparable to the metal complexes of distorted porphyrins and are much more inert than dipyrrolylmethenate mononuclear complexes.     

Control of the phase formation process in solutions of anionic polyelectrolyte—cationic surfactant complexes in a microfluidic channel

Russian Chemical Bulletin - The process of phase formation in solutions of polyacrylic acid and cetyltrimethylammonium bromide was studied in microfluidic channels with a characteristic size of...     

Kinetics of the dissociation of zinc(II) complexes with 3,3′-bis(dipyrrolylmethenes) in acetic acid-benzene binary solvent

A comparative study of the dissociation of zinc(II) helicates with a series of 3,3??-bis(dipyrrolylmethenes) (H₂L) of [Zn₂L₂] composition in acetic acid-benzene binary proton donor solvent in the temperature range from 298.15 to 318.15 K is performed by means of electronic spectroscopy. Quantitative kinetic characteristics are determined and a stoichiometric mechanism of reaction is suggested. It is established that the protolytic dissociation of [Zn₂L₂] helicates proceeds according to a third-order kinetic equation of reaction. The effect of alkyl substituents in the pyrrol rings and nature of central 3,3??-spacer on lability of helicates is analyzed.     

Catalytic oxidation of cyclohexene to cyclohexanone by a triple system in acidic aqueous acetonitrile medium

The catalytic oxidation of cyclohexene to cyclohexanone using Pd(OAc)2/HQ/FePc was investigated in an acidic aqueous solution of acetonitrile. The role of each component of this system in the oxidation of cyclohexene was explored by means of UV-VIS, IR, XPS spectroscopy and cyclic voltammetry, respectively. Based on the experimental results, the mechanism of the oxidation of cyelohexene catalyzed by Pd(OAc)2/HQ/FePc was elucidated.     

Association of ionic surfactant in binary water—ethanol media as indicator of changes in structure and properties of solvent

Russian Chemical Bulletin - Association of sodium dodecyl sulfate (SDS) ionic surfactant in concentration range of 1–100 mmol L?1 in binary water—ethanol media with alcohol volume...     

Kinetics and mechanism of oxidation of some nickel(II)–imine–oxime complexes by peroxodisulfate in aqueous acidic solutions

The kinetics of the oxidation of [Ni(II)(H₂L¹)](ClO₄)₂, (H₂L¹ = 3,8-dimethyl-4,7-diaza-3,7-decadiene-2,9-dione dioxime) and [Ni(II)(HL²)]ClO₄, (H₂L² = 3,9-dimethyl-4,8-diaza-3,8-undecadiene-2,10-dione dioxime) by peroxodisulfate anion (PDS) in aqueous media at 298.0 K have been studied. The kinetics of oxidation of both Ni(II) complexes was found to be first order in the complex concentration. The dependence of the pseudo-first-order rate constant, k _obs, for both complexes showed first-order dependence on PDS concentration. The kinetics of oxidation of [Ni(II)(H₂L¹)]²⁺ complex showed a complex dependence on [H⁺] over the pH range of 4.98–7.50, whereas that of [Ni(II)(HL²)]⁺ is independent of pH over the pH range of 5.02–7.76. The value of k _obs, for both complexes, decreased with increasing ionic strength consistent with the involvement of oppositely charged ions in the rate-determining step. The effect of ionic strength is more pronounced for [Ni(II)(H₂L¹)]²⁺–PDS reaction than for [Ni(II)(HL²)]⁺–PDS reaction, confirming the higher charges of the latter.     

Catalytic oxidation of aliphatic alcohols in the tetraaquapalladium(ii) complex—iron(iii)—dioxygen system

The selective low-temperature (40—70 °C) catalytic oxidation of methanol, propan-1-ol, and propan-2-ol in the presence of the tetraaquapalladium(ii) complex and iron(iii) ions and/or molecular oxygen as cooxidants was studied. The corresponding carbonyl compound is the product of alcohol oxidation. The kinetic regularities of the reaction were established. In the reaction mechanism proposed, the key step is palladium(i) formation.     

The role of low levels of water in the electrochemical oxidation of α-tocopherol (vitamin E) and other phenols in acetonitrile

The phenol, α-tocopherol, can be electrochemically oxidised in a -2e(-)/-H(+) process to form a diamagnetic cation that is long-lived in dry organic solvents such as acetonitrile and dichloromethane, but in the presence of water quickly reacts to form a hemiketal. Variable scan rate cyclic voltammetry experiments in acetonitrile with carefully controlled amounts of water between 0.010 M-0.6 M were performed in order to determine the rate of reaction of the diamagnetic cation with water. The water content of the solvent was accurately determined by Karl Fischer coulometric titrations and the voltammetric data were modelled using digital simulation techniques. The oxidation peak potential of α-tocopherol measured during cyclic voltammetry experiments was found to shift to less positive potentials as increasing amounts of water (0.01-0.6 M) were added to the acetonitrile, which was interpreted based on hydrogen-bonding interactions between the phenolic hydrogen atom and water. Several other phenols were examined and they displayed similar voltammetric features to α-tocopherol, suggesting that interactions of phenols with trace amounts of water were a common occurrence in acetonitrile. The H-bonding interactions of α-tocopherol with water were also examined via NMR and UV-vis spectroscopies, with the voltammetric and spectroscopic studies extended to include other coordinating solvents (dimethyl sulfoxide and pyridine).     

Polymerization of 5-norbornene-2-methyl acetate catalyzed by air-stable cationic (η-substituted allyl) palladium complexes of N-heterocyclic carbene

In situ generated cationic (η³-substituted allyl) palladium N-heterocyclic carbene (NHC) complexes are air-stable active catalysts for the olefin polymerization of (bicyclo[2.2.1]hept-5-en-2-yl)methyl acetate (5-norbornene-2-methyl acetate) (endo:exo = 7:3). Catalytic activities, polymer yields, molecular weights, and molecular weight distributions of polymers were investigated under various reaction conditions. The catalytic activity was highly dependent not only on the reaction condition such as a solvent or the reaction temperature but also on the structure of the catalyst that include substituents of the allyl group in the catalyst and the counter anion. As the bulkiness of the allyl group increased, the catalytic activity of the catalysts increased.     

Supramolecular networks constructed by cationic copper(II) complexes incorporating hybrid water–anionic polymeric assemblies

Two complexes, [Cu₂(TFSA)(2,2′-bpy)₄]?·?TFSA?·?8H₂O (1) and {[Cu(4,4′-bpy)(H₂O)₂]?·?TFSA?·?6H₂O} _n (2) (H₂TFSA?=?tetrafluorosuccinic acid, 2,2′-bpy?=?2,2′-bipyridine, and 4,4′-bpy?=?4,4′-bipyridine), have been synthesized and structurally characterized by X-ray structural analyses. Complex 1 is a binuclear molecule bridged by TFSA ligands; 2 is a 1-D chain bridged by 4,4′-bpy ligands. The asymmetric units of the two complexes are composed of cationic complexes [Cu₂(TFSA)(2,2′-bpy)₄]²⁺ (1) and [Cu(4,4′-bpy)(H₂O)₂]²⁺ (2), free TFSA anion, and independent crystallization water molecules. A unique 2-D hybrid water–TFSA anionic layer by linkage of {[(H₂O)₈(TFSA)]^2?} _n fragments consisting of 1-D T6(0)A2 water tape and TFSA anionic units by hydrogen bonds in 1 was observed. Unique 2-D hybrid water–TFSA anionic layer generated by the linkage of {[(H₂O)₆(TFSA)]^2?} _n fragments consisting of cyclic water tetramers with appended water molecules and TFSA anionic units, and 1-D metal–water tape [Cu–H₂O?···?(H₂O)₆?···?H₂O^?] _n in 2 were found. 3-D supramolecular networks of the two complexes consist of cationic complexes and water–TFSA anionic assemblies connected by hydrogen bonds.     

Spectrochemical properties of noncubic transition metal complexes in solutions—IV. Energy levels of tetragonal distorted chromium(III) complexes in aqueous solutions

A general method for the analysis of the d-d transition energies observed in the ligand field spectra of chromium(III) complexes with D_4h or C_4υ symmetry is described and used to derive the crystal field and angular overlap parameters for the complexes of known stereochemistry. Examples are also presented. The spectrum of the diamminetetrakis(isothiocyanato)chromate(III) ammonium in aqueous solution is reported. The spectra of the miscellaneous systems have been studied theoretically using a crystal field model and an angular overlap model.     

Oxidation of Fursemide by Diperiodatocuprate(III) in Aqueous Alkaline Medium—a Kinetic Study

Fursemide is the chemical compound 4-chloro-2-(furan-2-ylmethylamino)-5-(aminosulfonyl) benzoic acid. It was oxidized by diperiodatocuprate(III) in alkali solutions, and the oxidation products were identified as furfuraldehyde and 2-amino-4-chloro-5-(aminosulfonyl) benzoic acid. The reaction kinetics were studied spectrophotometrically. The reaction was observed to be first order in [oxidant] and fractional order each in [fursemide] and [periodate], whereas added alkali retarded the rate of reaction. The reactive form of the oxidant was inferred to be [Cu(H₃IO₆)₂]⁻. A mechanism consistent with the experimental results was proposed, in which oxidant interacts with the substrate to give a complex as a pre-equilibrium state. This complex decomposed in a slow step to give a free radical that was further oxidized by reaction with another molecule of DPC to yield 2-amino-4-chloro-5-(aminosulfonyl) benzoic acid and furfuraldehyde in a fast step. This reaction was studied at 25, 30, 35, 40 and 45 °C, and the activation parameters E _a,ΔH ^#,ΔS ^# and ΔG ^# were determined to be 51 kJ⋅mol⁻¹,48.5 kJ⋅mol⁻¹,−63.5 J⋅K⁻¹⋅mol⁻¹ and 67 kJ⋅mol⁻¹, respectively. The value of log ₁₀ A was calculated to be 6.8.     

Raman spectral studies on solutions of lithium bromide in binary mixtures of water and acetonitrile in the CH and CN stretching regions

Raman spectra of solutions of LiBr in mixtures of acetonitrile and water of varying compositions are reported. The symmetric CH stretching and CN stretching bands of acetonitrile are used as probes to study the ion molecular interactions. The full width at half maximum (FWHM) and frequency shifts of the bands under consideration are analysed. Vibrational correlation functions for the CH₃ stretching mode are computed and vibrational relaxation times are evaluated for additional information. The results are explained on the basis of ion-molecular interactions in general and preferential solvation of Br⁻ ions by water in particular.     

Solvation behaviour of silver(I) iodate in methanol—acetonitrile and ethanol—acetonitrile mixtures

The solvation behaviour of silver(I) iodate in methanol—acetonitrile (AN) and ethanol—acetonitrile mixtures has been studied at 30°C by solubility and emf measurements. The solubility of the salt increases with the addition of AN and passes through a maximum at X_AN = 0.3 and 0.6 in the case of MeOH-AN and EtOH-AN mixtures, respectively, and then decreases with further addition of AN. The transfer free energy of silver ion decreases while that of iodate ion increases with the addition of AN in both the solvent mixtures. The solvent transport number, Δ of AN is positive with a maximum at X_AN = 0.45 (Δ = 0.45 (Δ = 5.4) and at X_AN = 0.55 (Δ = 2.4) in the case of MeOH-AN and EtOH-AN mixtures, respectively. These results have been interpreted in terms of the heteroselective solvation of the salt, the silver ion being preferentially solvated by AN and the iodate ion by the amphiprotic solvent component in these mixtures.     

Suzuki–Miyaura cross-coupling reactions in water using in situ generated palladium(II)–phosphazane complexes

The phosphazane derivatives(L1–3) were readily obtained by reaction of different ratios of PCl3 and PhNH2. The L1–3 derivatives were found to be efficient ligands in the palladium-catalyzed Suzuki C–C coupling reactions in water. It was determined that with the use of L1–3 /Pd(OAc)2 system as a catalyst, aryl halides undergo Suzuki cross-couplings with arylboronic acids to give the desired products in moderate to excellent yields.     

Effect of the composition of dimethyl sulfoxide–acetonitrile solvent on the stability of silver(I) complexes with 2,2'-bipyridyl

The effect of composition of the dimethyl sulfoxide–acetonitrile solvent on the shift in complexation equilibrium of silver(I) and 2,2'-bipyridyl was studied potentiometrically at 298.15 K. The stability of mono- and bis(bipyridyl) complexes of silver(I) was found to rise with increasing acetonitrile content in the mixed solvent. The difference in changes in the solvation state of the central and complex ions (the solvation effect of ions) was found to make a major contribution to the changes in stability of silver(I) complexes with 2,2'-bipyridyl in dimethyl sulfoxide–acetonitrile binary solvent.     

Synthesis of Co–Pd alloys by co-electroreduction of aquachloro-cobalt(II) and palladium(II) complexes

The work presents results of the studies on the synthesis of Co–Pd alloys from acid electrolytes containing chloride ions. The main aim of the tests was to identify reactions responsible for alloy formation and to determine an influence of the electrolysis parameters, i.e. working electrode potential, electrolyte composition and temperature on the composition of the resulted alloy coatings. Electrochemical investigations were performed by applying cyclic voltammetry (CV) combined with electrochemical quartz crystal microbalance (EQCM). The electrolyte composition was selected based on a thermodynamic analysis and spectrophotometric tests which were described in our previous papers [1, 2]. They allowed determination of equilibrium distribution of the metals complex forms and a stability analysis of the electrolyte. The alloys were synthesized within the potential range from ?0.7 to ?1.1 V. The tests indicate a possibility of alloys synthesis already at the potential range 相似文献