Pressure effects on the rate of electron transfer between tris(1,10-phenanthroline)iron(II) and -(III) in aqueous solution and in acetonitrile

Abstract

HIDEO DOINE and THOMAS WILSON SWADDLE. Can. J. Chem. 66, 2763.Proton nrnr line-broadening experiments at ambient and elevated (to 215 MPa) pressures show that the rate of electron transfer between F e (~h e n )~~+ and Fe(phen)33+ as bisulfates in D20/D2S04 is represented by the activation parameters (at ionic strength I -0.4molkg-I) AH* = 1.6 ? 0.5kJmol-I, AS* = -102.2 ? 1.6 J K -~~o I -' , k(276K) = 1.31 x 107kgmol-Is-', and (at I -0.3 mol kg-' and a mean pressure of 100 MPa) AV* = -2.2 2 0.1 cm3 mol-I. For the same reaction of the perchlorate salts (total [Fe] 0.046-0.065 mol kg-') in CD3CN, AH* = 11.0 I+-1.0 kJ mol-I, AS* = -72.5 2 3.6 J K-I mol-I, k(277 K) = 8.0 X 106kg mol-I s-I, and AV* = -5.9 2 0.5 cm3 mol-l. For water as solvent, AV* is satisfactorily accounted for by a classical theory of the Stranks-Hush-Marcus type. Volumes of activation for electron self-exchange are shown to provide criteria for non-adiabaticity and for dominance of (non-aqueous) solvent reorganizatlon dynamics; on this basis, it is seen that neither of these factors is important in the title reactions.HIDEO DOINE et THOMAS WILSON SWADDLE. Can. J. Chem. 66, 2763.Des experiences d'klargissement de raies dans les spectres rmn du proton, effectuies a la pression ambiante et a des pressions allant jus u'i 215 MPa, permettent de demontrer que la vitesse de transfert d'Clectron, entre les ions Fe(phen)32+ et le 4 . . 0,l cm3 mol-'. Lorsque l'eau est le solvant, on peut facilement expliquer la valeur du AV* par une thCorie classique du type Stranks-Hush-Marcus. On dCmontre que les volumes d'activation pour l'auto-Cchange des electrons fournissent des critkres pour expliquer les propriCtCs non-adiabatiques ainsi la dominance de la dynamique de reorganisation des solvants non-aqueux; sur cette base, on peut comprendre pourquoi aucun de ces facteurs n'est important dans les reactions mentionnCes dans le titre.[Traduit par la revue]

Variable-pressure dynamic NMR studies: effects of paramagnetic metal ions on NMR parameters in nonexchanging systems

“…Thus, activation volumes for exchange reactions, obtained from line-broadening measurements using 'H or other spin-112 nuclei, may be reliable within experimental accuracy even without correction for the extra broadening caused by the outersphere interactions between the observing nucleus and a paramagnetic solute, which is consistent with experience in previous studies (2,6,12). On the other hand, when quadrupolar nuclei are used for the observation of exchange kinetics, volumes of activation obtained by high-pressure NMR methods may not be valid without corrections for the pressure dependence of the natural line widths using the method described here.…”

“…The chemical shift of the methyl proton signal relative to that of the internal benzene signal as a reference was not affected by the applied pressure up to 200 MPa. Benzene was chosen as a reference material as little or no interaction with Cr(acac), was found in previous studies (12).…”

Pressure dependences of the electrode potentials of some iron(III/II) and cobalt(III/II) couples in aqueous solution

“…The iron couples were chosen with the expectation that they would yield information on the influence of ionic size, charge, and spin state on the pressure response of the electrode potentials, while the cobalt(III/II) sepulchrate couple was included as an ideal example of an obligate outersphere low-spin/high-spin electrode transfer system, since neither the cobalt(II1) nor the normally labile cobalt(I1) ion can escape from the robust encapsulating ligand. For our present purposes, however, the most important consideration is that the pressure dependences of the kinetics of the self-exchange reactions of all four couples have been reported (1)(2)(3)(4)(5)(6) and the use of those data together with the present results in testing the applicability of the Marcus "cross 'To whom all correspondence should be addressed coming article. A variety of approaches to measurements of electrode phenomena at high pressures have been reported (5,6,(8)(9)(10)(11)(12)(13)(14)(15).…”

“…This phenomenon might be attributed, at least in part, to the increase in solvent electrostriction (17) expected for the effective net reaction [4] Can. J. Chem.…”

“…Iron(II1) perchlorate hydrate (Aldrich, low chloride) was converted to the tfluoromethanesulfonate salt in aqueous CF3S03H by addition of CF3S0,K to precipitate KC10,; the iron concentration was determined spectrophotometrically with 1,lOphenanthroline after reduction to iron(II) with hydroxylamine, and the hydrogen ion concentration by titration with alkali. Cobalt(II1) sepulchrate chloride monohydrate and tris(1,lO-phenanthro1ine)-iron(I1) sulfate 9-hydrate were made and checked for purity as described elsewhere (2,4). All other reagents were of analytical reagent quality, and distilled water was passed through a Barnstead NANOpure purification train before use.…”