David R. Rosseinsky

Kinetics and mechanism of the formation of manganese(III) from manganese(II) and (VII) in aqueous perchlorate solution

The reaction 4MnIIfMnVxI = 5MnIII obeyed the rate equation, rate = k[Mnu]2[MnvII]. In lithium perchlorate media the [H+]-dependence was found to be k = k~H+]+ko. Activation energies and entropies were compared with standard values for formation of intermediate species in an examination of possible mechanisms.

Kinetics of the aqueous manganese(III)+ iron(II) reaction by platinum-electrode polarography

The rate equation –d[FeII]/dt=kobs[FeII][MnIII] was established by measurements of the iron(II) diffusion current. For 0.3–15°C in 0.54-3 M HClO4 the variation of kobs was consistent with the relation kobs=(ko[H+]+k1Kh)/([H+]+Kh), where Kh is the manganese(III) hydrolysis constant. Values of k0 are just less than k1 as in the comparable oxidation of vanadium(IV). It is concluded from further comparisons of rates that the activated complexes are outer-sphere.

Inter- and intra-molecular quenching of anthracene fluorescence by pyridinium ion in solution

The compound 1-(9-anthrylmethyl)pyridinium chloride contrasts with most anthracene derivatives in showing no fluorescence. It is established that the anthracene fluorescence is quenched at a diffusion controlled rate by pyridinium ion, indicating that the non-fluorescence of the compound results from a quasi-free interaction of the attached pyridinium moiety. Corrections for internal absorption are clarified.

The iron(II)–chromium(VI) reaction: an additional pathway first order in iron(II)

The iron(II)–chromium(VI) reaction has been studied by platinum-electrode polarography at low (micromolar) iron(II) concentrations. Here an additional term first order in iron(II) appears in the rate equation, which is found to be –d[FeII]/dt=k1H[H+][HCrO4–][FeII]+k2H[HCrO4–][FeII]2/[Fe3+], with k1H= 234 l2 mol–4 s–1 and 10–8k2H= 6·92 l4 mol–4 s–1 at 20 °C and ionic strength 1·00 mol l–1 in sodium perchlorate medium with 0·025–0·065M perchloric acid.

Electron-transfer kinetics of the iron (II)-vanadium (V), iron (III)-vanadium (IV) system in aqueous perchlorate, by platinum-electrode polarography

Separate measurements of forward and reverse reaction rates of the reaction Fe(II)+V(V)⇄Fe(III)+V(IV)Fe(II)+V(V)⇄Fe(III)+V(IV) have been obtained at several temperatures by measurements of the Fe(II) diffusion current. These confirm that the major paths have rate terms respectively proportional to and inversely proportional to [H +], although medium effects are also apparent. An interpretation of the very low ΔH1* (1·69 Kcal/mole) for the major foward path is given in terms of a proton transfer coefficient.

Kinetics of cobalt(III)+ iron(II) reaction by platinum-electrode chronoamperometry in aqueous perchloric acid solution

The rate of the CoIII+ FeII reaction in 3 mol dm–3 HClO4 is obtained by amperometry and confirms (corrected) results from stopped-flow experiments. Three current questions about the state and reactivity of CoIII are discussed and partly resolved; in particular E° for CoIII/CoII is confirmed as being 1.8–1.9 V.

Comparison of the excimer fluorescence of (-) bornyl-9- anthryl-3-propanoate in solution and solid state

The normal temperature dependence of solution excimer fluorescence (maximum Dm) and the enthalpy ΔH of excimer formation of the title compound contrast with the temperature effect on the solid fluorescence. In explanation it is suggested that the repulsion is a bound-twisting effect different from (shallower but extending further than) the more usual electron-overlap repulsion. Dm and the monomer maximum are at 18,500 and 25,500 cm-1 respectively; ΔH is 12.8 k J mol-1.

Kinetics and mechanism of the reduction of manganese(III) in perchloric acid at a platinum electrode

The electrode kinetics at 25°C of the reduction of manganese(III) on an oxidised platinum surface confirms an unusually low transfer coefficient of 0.26. Interpretation involving a comparison with a correlation of hydrolytic constants of similar trivalent cations and their several redox potentials points to a hydroxo-or oxo-bridged transition state. The MnIII/MnII conditional standard electrode potential was observed to be 1.535 V at ionic strength 3.31 mol dm–3 against H2|HClO4(3 mol dm–3), NaClO4(0.31 mol dm–3).

Manganese(III) and its hydroxo- and chloro-complexes in aqueous perchloric acid: comparison with similar transition-metal(III) complexes

At 25°C the formation constant of MnCl2+ is found by spectrophotometry to be 13.2 ± 0.9 dm3 mol–1 at ionic strength 3.26 mol dm–3; for MnCl+2 the value is 1.1 ± 0.7 dm3 mol–1. Increase in the number of chloride ions in complexes results in longer wavelengths for the corresponding absorption maxima. In the absence of chloride the hydrolysis constant of MnIII at ionic strength 5.6 mol dm–3 is found from voltammetry and potentiometry to be 1.05± 0.26 mol dm–3. Aged managanese(III) is found to be 15–25% polymeric, from both kinetic and e.m.f. measurements. Comparison of formation constants for halogeno- and hydroxo-complexes of M3+(first transition series) shows that a combination of charge-transfer, ligand-field and coulomb interactions underlies the observed sequences; the dipole moment of OH– is also a factor.

Semiconductor properties of crystalline anthracene. Competition of electron and hole photoinjection by redox electrolytes

Electron photocurrents have been measured with a number of solution photoinjectors. A new set of electrode potentials for solid anthracene is used to account for the pH dependence of electron as compared with hole photocurrents and the absence of limiting values for the former, in terms of the reducibility and oxidisability of anthracene and the relative probabilities of charge reversion to the electrolyte injectors. The magnitudes of electron currents can in most cases be correlated with change-transfer properties of the injectors or heavy atom spin-orbit effects on intersystem crossing.