Pilar Guardado

Solubilities of salts and kinetics of reaction between hydroxide ions and iron(II)–di-imine complexes in water–methanol mixtures. Derivation of single-ion transfer chemical potentials and their application to analysis of solvent effects on kinetic parameters

Kinetic data are reported for the reaction at 298 K and ambient pressure between two iron(II)–di-imine complex cations and hydroxide ions in water–methanol mixtures. Solubility data are reported for a range of inorganic salts containing simple and complex ions. Methods for calculating transfer chemical potentials of single ions are examined and, depending on the extrathermodynamic assumption, shown to predict different trends in the properties of ions in these aqueous mixtures. Further, calculated initial- and transition-state solvation effects on the kinetics are different: in some cases dramatically so. The solvation characteristics are compared for various ions in methanol–water mixtures as calculated using the tetraphenylphosphonium tetraphenylborate (TPTB) assumption, which sets the transfer chemical potential of tetraphenylphosphonium ions equal to that of tetraphenyl-boronate ions. Arguments are advanced for adopting single-ion transfer chemical potentials based on this assumption. Relationships are examined between the transfer parameters for H+, H3O+, ROH+2 and H9O+4 ions in binary aqueous mixtures, ROH + H2O.

Pressure and solvent effects on the rate of the reaction of tricarbonylcycloheptatrienoneiron with tetracyanoethene

Abstract Pressure and solvent effect studies on the reaction of tricarbonylcycloheptatrienoneiron with tetracyanoethene support a concerted mechanism for the reaction.

Transfer chemical potentials for ions, solubilities of salts and kinetics of reactions involving inorganic complex ions at ambient pressure and 298.2 K in binary aqueous mixtures containing ethanol and propan-2-ol

Solubilities of several complex salts at ambient temperature and pressure are reported for aqueous solutions and for solutions in binary aqueous organic mixtures. The organic cosolvents are ethanol and propan-2-ol. These and earlier published solubilities are analysed using the TATB assumption which sets the transfer chemical potentials of Ph4As+ ions equal to those of Ph4B– ions. The calculations yield transfer parameters for various ions including complex metal ions. Derived transfer parameters for ions are compared for a range of solvent systems comprising binary aqueous mixtures, including those systems where the organic cosolvents are methanol, ethanol, propan-2-ol and acetone. These transfer parameters are used in an analysis of kinetic data describing chemical reaction between hydroxide ions and iron(II) complex cations, [Fe(phen)3]2+ in aqueous solutions. Definitions of standard state chemical potentials for solutes and solvents are considered with reference to descriptions of composition of these systems using the mole fraction scale.

Guest–host interactions between tetrahydrobetacarboline and β-cyclodextrin

The interactions between 1,2,3,4-tetrahydro-9H-pyrido[3,4-b]indole or tetrahydrobetacarboline, THBC, and cycloheptaamilose or β-cyclodextrin, β-CD, have been investigated using UV absorption, steady state and time resolved fluorescence measurements. The addition of β-cyclodextrin has very little effect on the absorption spectra of neutral and cationic THBC species. However, it induces a blue shift and pronounced fluorescence enhancements in the emission spectrum of the neutral substrate. Both, steady state and time resolved fluorescence studies show that neutral THBC species form 1:1 inclusion complexes with β-CD. Global analysis of the time resolved data provides evidence on the formation of two different types of 1:1 THBC–β-CD complexes. It is assumed that each one of these complexes corresponds to the two different topologies for the entry of the THBC molecule into the β-CD cavity, i.e. by its benzene or by its piperidinic moiety. Association constants of the complexes and other thermodynamic and photophysical parameters have been estimated from fluorescence measurements.

Isomeric forms of tris-Schiff base complexes of iron(II) : structure of the complex derived from 2-acetyl pyridine and methylamine

SummaryThe structure of the tetrahydrate of the nitroprusside salt of the tris-ligand-FeII complex of the Schiff base derived from 2-acetyl pyridine and methylamine has been established by x-ray diffraction methods. The cation has themer-configuration in this salt in the solid phase. Kinetic and spectroscopic, particularly1H n.m.r., results indicate that bothmer-andfac-isomers of this, and of related complexes, have to be considered in solution. Kinetics of base hydrolysis of the title cation, and its solvation, in MeOH-H2O mixtures are described and compared with those for other low-spin FeII-diimine complexes.

Solvent and pressure effects on intramolecular electron transfer rates within a binuclear cobalt(III)pyrazine carboxylateiron(II) anion

Abstract Rate constants are reported for intramolecular electron transfer within the pyrazine carboxylate bridged dinuclear complex [(en) 2 Co(pzc)Fe(CN) 5 ] − in aqueous methanol, 0 to 80% (by volume) methanol. Activation volumes for this process in water and in 60% methanol are +24 and +7 cm 3 mol −1 respectively. Rate constant trends and activation volumes are discussed in terms of medium dielectric properties and of solvation of the initial state and of the activated complex for electron transfer.

Oxidation of 2,3-dimethylindole by peroxophosphates

The kinetics of the oxidation of 2,3-dimethylindole 1 by peroxodiphosphoric, PDP, and peroxomonophosphoric, PMP, acids have been investigated in sulfuric acid (0.1–1 mol dm–3) and 20%v/v methanol–water solutions. On the basis of the spectral and kinetic results and by analogy with the mechanism previously proposed for the oxidation of 1 by peroxomono- and peroxodi-sulfate anions, we have concluded that the reactions proceed through the following steps: an electrophilic attack of the peroxide bond at the C-3 atom of the indole ring to form an indoleninic intermediate, a second peroxo attack on the enaminic tautomer of this intermediate and the hydrolysis of the product to finally give 3-methylindole-2-carbaldehyde. The analysis of the dependence of the reaction rates with acidity shows that, under our experimental conditions, neutral H4P2O8 and cationic H4PO5+ are, respectively, the active species mainly involved in the oxidation processes.

Solvation and reactivity of iron(II)–diimine complexes in dimethyl sulfoxide–water mixtures

Kinetics of the base hydrolysis of several iron(II)–diimine complexes, including two with terdentate ligands and one with an encapsulating ligand, and of the peroxodisulfate oxidation of three ternary iron(II)–diimine–cyanide complexes, are reported for reaction in dimethyl sulfoxide (DMSO)–water mixtures at 298.15 K. Solubilities of simple and complex salts have been determined in these mixtures, both to extend the range of simple and complex ion-transfer chemical potentials and to provide the basis for initial-state/transition-state analyses of reactivity trends for several of the base hydrolysis and peroxodisulfate oxidations. Cases are identified where the destabilisation of hydroxide ions, OH–(aq), by added DMSO increases the rate of base hydrolysis. We also identify cases where compensation effects result in only a small change in rate constant for oxidation by peroxodisulfate where DMSO is added.

Solvation of iron and chromium complexes in alcohol-water mixtures

Solubilities are reported for the perchlorates of five iron(II)-diimine complexes in t-BuOH–H2O and one in MeOH–H2O mixtures, for three iron(III)-3-hydroxy-4-pyranonate and three iron(III)-3-hydroxy-4-pyridinonate complexes in MeOH–H2O and t-BuOH–H2O, and for two chromium(III)-3-hydroxy-4-pyranonate complexes in MeOH–H2O. Transfer chemical potentials are thence derived for the various iron(II), iron(III) and chromium(III) complexes, for transfer from H2O into the respective mixed solvents (at 298.2 K). These results are combined with values reported earlier for related complexes, and for other alcohol–H2O mixtures, to give an overall picture of solvation, expressed in the thermodynamic format of transfer chemical potentials, for iron(II)-diimine, iron(III)-3-hydroxy-4-pyridinonate and chromium(III)-3-hydroxy-4-pyranonate complexes in H2O-rich aqueous-alcohol mixtures. Some spectroscopic (1H-n.m.r.; i.r.) and kinetic (aquation rate constants at 298.2 K) data are reported for the chromium(III) complexes.

Solvation and reactivity of tris(diimine)–iron(II) complexes in aqueous ethane-1,2-diol, propane-1,2,3-triol and sucrose

The dependence of rate constants for base hydrolysis on solvent composition for several iron(II)–diimine complexes has been established for aqueous ethane-1,2-diol (ethylene glycol) and aqueous propane-1,2,3-triol (glycerol) mixtures, and for aqueous sucrose solutions. These dependences are compared with analogous reactivity trends for binary aqueous solvent mixtures containing monohydroxylic alcohols. Transfer chemical potentials for iron(II)–diimine complexes, and for simple cations and anions, have been estimated on the TATB assumption for transfer to aqueous ethane-1,2-diol and aqueous propane-1,2,3-triol. These transfer chemical potentials allow resolution of the observed reactivity trends into initial-state and transition-state contributions for the aqueous ethane-1,2-diol mixtures. Such information on the role of solvation in this type of reaction is complented by the determination of activation volumes for base hydrolysis for four iron(II)–diimine complexes in aqueous ethane-1,2-diol.