Electrode reactions of metal complexes in solution at high pressures

Techniques for measuring the pressure dependencies of the electrode potenti als (characterized by the cell reaction volume Delta V-cell) and electrode kinetics (volume of activation Delta V-double dagger) of metal complexes ar e described. Volumes of reaction Delta V for net redox reactions can be obt ained by the combination of Delta V-cell values. We show how Delta V-cell c an be broken down into contributions of the couple of interest and the refe rence electrode, and how the solvational and intrinsic components of the fo rmer can be evaluated. Values of Delta V-double dagger measured for electro de reactions of aqueous metal complex couples are precisely one-half of the Delta V-double dagger found for the corresponding outer-sphere self-exchan ge reactions, and can generally be accounted for by an extension of Marcus theory developed for the latter. When Delta V is known, the theory can be e xtended to Delta V-double dagger for redox 'cross' reactions; thus, Delta V -double dagger can serve as a criterion of a simple, adiabatic, outer-spher e reaction mechanism. (C) 1999 Elsevier Science S.A. All rights reserved.