Ruthenium and iron complexes with benzotriazole and benzimidazole derivatives as simple models for proton-coupled electron transfer systems

iron and ruthenium complexes of the type [m-lh]n (where m = ruii,iii(nh3)5 2+,3+, ruii,iii(edta)2-,- [edta = ethylenedinitrilotetraacetate], or feii,iii(cn)53-,2- and lh = benzotriazole or benzimidazole) were prepared and characterized in aqueous solutions by means of electrochemical and spectroelectrochemical methods. special emphasis was given to the ph-dependent redox processes, exhibited by all the investigated complexes. from their related pourbaix diagrams, which displayed a typically nernstian behavior, the pka and formal reduction potential values were extracted. in addition, these e1/2 versus ph curves were also used to illustrate the partitioning relationship concerning the redox and acid-base species, and their interconversion equilibria. the active area in which the dependence of the miii/mii couple on the ph takes place, as delimited by pkaiii and pkaii, was taken into account in order to evaluate the usefulness of such simple complexes as models for proton-coupled electron transfer (pcet). the results were interpreted in terms of the acceptor/donor electronic character of the ligands and s,p-metal-ligand interactions in both redox states of the metal ion.