Nicholas J. Blundell

An inverse Kirkwood–Buff treatment of the thermodynamic properties of DMSO–water mixtures and cyanomethane–water binary liquid mixtures at 298.2 K

The dependence on mole fraction of GEm for DMSO(2)–water(1) mixtures has been analysed using the Redlich–Kister equation. Derived parameters and other properties of this system have been used to calculate Kirkwood–Buff integral functions G11, G22 and G12 which are related to spatial correlation functions for the liquid mixture. Trends in these parameters as a function of mole fraction composition point to the importance of the function G12 consistent with strong intercomponent hydrogen bonding. The dependence of GEm on x2 for water(1)—cyanomethane(2) mixtures is analysed using both Redlich–Kister and orthogonal polynomial functions. At 298.2 K and ambient pressure GEm > RT/2 for x2≈ 0.4 which, for a quadratic mixture, signals partial miscibility. This complexity impinges on the analysis which requires the second differential d2GEm/dx22. Parameters derived from the dependence of GEm on x2 using orthogonal polynomials are combined with other properties of this mixture to yield the Kirkwood–Buff integral functions. In contrast to DMSO–water mixtures, the dominant terms, G11 and G22, confirm the microheterogeneity of cyanomethane–water mixtures, where x2≈ 0.3.

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.

Ultrasonic absorption properties and Kirkwood–Buff integral functions for hydrogen peroxide–water and propanone–water mixtures at 298.2 K

Kirkwood–Buff integral functions for water(1)–propanone(2) binary liquid mixtures have been calculated from their thermodynamic properties and used in highlighting the dependence of sound absorption properties on mole fraction, x2, of the organic liquid component. At low x2, the dependence of the integral function G22 on x2 points to hydrophobic association, but this trend is overwhelmed as x2 increases by a dominant G11 which points to a degree of microheterogeneity of the mixture at 298.2 K and ambient pressure. These trends are compared with the dependence on mole fraction of the integral functions for water(1)–hydrogen peroxide(2) mixtures. In the latter system, the key quantity is G12, consistent with strong intercomponent interactions.

Oxidation of benzenediols by the iron(III) tetracyano bipyridyl ion: a high pressure stopped-flow kinetics study

Abstract The iron(III) tetracyano 2,2-bipyridyl ion, [Fe(CN)4(bpy)]−, readily oxidizes the benzenediols, catechol (1,2-dihydroxybenzene), 4-tertiary butyl catechol (1,2-dihydroxy-4-t-Bu-benzene), and methyl hydroquinone, (2-methyl-1,4-dihydroxybenzene) in aqueous solution. The kinetics have been studied by stopped-flow spectrophotometry in the pH range 2.5–6. At the lower end of this region the reactions are pH independent, and yield second order rate constants at 298.2 K of 50, 68 and 477 mol−1 dm3 s−1 for the three diols, respectively. In the pH dependent region (3–6) the rates, in buffered solution, vary due to the presence of differently protonated species of the iron(III) complex. Application of pressure, up to 1 kbar, gives rise to more rapid oxidation, and within experimental error, the volume of activation, ΔV* is substrate independent (ΔV* = −18 cm3 mol−1). The values of ΔS* are compatible with this finding. Kinetic and activation parameters are treated within the framework of an outer-sphere electron transfer mechanism.

Hexachloroiridate(IV) oxidation of benzenediols in binary aqueous solvent mixtures: Solvation and reactivity

Abstract Kinetic parameters are reported for hexachloroiridate (IV) oxidation of t-butyl-catechol (4-t-butyl-benzene-1,2-diol), hydroquinone (benzene-1,4-diol) and its 2-t-butyl derivative in binary aqueous mixtures containing methanol, ethanol, t-butyl alcohol, acetone, dimethyl sulfoxide, or dimethylformamide. Solubilities are reported, and transfer chemical potentials thence derived, for hydroquinone in a range of such media and for catechol, 2,4-bis-(t-butyl)catechol, methylhydroquinone and t-butyl- hydroquinone in methanol-water mixtures. On the basis of a selection of these kinetic and thermodynamic rnyesults we have analysed reactivity trends for several of these hexachloroiridate(IV) oxidations into initial state and transition state contributions.

Solvatochromism and piezochromism of dicyano-, tricyano-, and tetracyano-diimine-iron(II) complexes

The solvatochromism of several dicyano-bis-diimine-iron(II) complexes in various binary aqueous solvent mixtures has been established, at 25 °C. A solvent sensitivity scale has been developed for these complexes. The solvatochromic properties of two tricyano-terdentate ligand iron(II) complexes in several solvents have also been determined, as have those of a series of tetracyano-diimine complexes in DMSO–water media. These results have been analysed and systematic but varied trends of solvation were demonstrated. Piezochromic parameters for two complexes have been obtained and are discussed in the context of a solvatochromism/piezochromism correlation.

Analysis of solvent effects on the kinetics of alkaline hydrolysis of an iron(II) complex using the Kirkwood–Buff treatment of preferential solvation

Trends in Kirkwood–Buff integral functions for initial and transition states associated with the reaction of [Fe(phen)3]2+ complex cations (phen = phenanthroline) with OH– anions in water/methyl alcohol mixtures identify the role of preferential solvation in determining the dependence of rate constant on solvent composition.

Solvation and reactivity in the ferrocene-ferricinium electron exchange reaction

Abstract The remarkably small solvent effect on reactivity for the ferrocene-ferricinium electron exchange reaction, unexpected on the basis of Marcuss theory, is analysed into initial state and transition state contributions with the aid of published kinetic data and new solubility measurements. This analysis has been conducted on the basis of the tetraphenylarsonium- tetraphenylboronate (TATB) and ferrocene- ferricinium (fc/fc+) assumptions.

Partial molar volumes for tetracyano(diimine)ferrate(II) anions in aqueous solution

Partial molar volumes have been determined by density measurements for a series of salts K2[Fe(CN)4-(diimine)]. The values for the anions are discussed in relation to analogous tris(diimine)iron(II) cations, and to other inorganic complexes.