Collect. Czech. Chem. Commun. 2009, 74, 1543-1557
Published online 2009-12-09 23:28:25

Protonation effects on dynamic flux properties of aqueous metal complexes

Herman P. Van Leeuwena,* and Raewyn M. Townb

a Laboratory of Physical Chemistry and Colloid Science, Wageningen University, Dreijenplein 6, 6703 HB Wageningen, The Netherlands
b Institute for Physics and Chemistry, University of Southern Denmark, Campusvej 55, 5230 Odense, Denmark


The degree of (de)protonation of aqueous metal species has significant consequences for the kinetics of complex formation/dissociation. All protonated forms of both the ligand and the hydrated central metal ion contribute to the rate of complex formation to an extent weighted by the pertaining outer-sphere stabilities. Likewise, the lifetime of the uncomplexed metal is determined by all the various protonated ligand species. Therefore, the interfacial reaction layer thickness, μ, and the ensuing kinetic flux, Jkin, are more involved than in the conventional case. All inner-sphere complexes contribute to the overall rate of dissociation, as weighted by their respective rate constants for dissociation, kd. The presence of inner-sphere deprotonated H2O, or of outer-sphere protonated ligand, generally has a great impact on kd of the inner-sphere complex. Consequently, the overall flux can be dominated by a species that is a minor component of the bulk speciation. The concepts are shown to provide a good description of experimental stripping chronopotentiometric data for several protonated metal–ligand systems.

Keywords: Eigen mechanism; Dynamic metal speciation; Association rate; Dissociation rate.

References: 45 live references.