Proton-induced switching and control of intramolecular electron transfer on a benzotriazole-bridged symmetric mixed-valence ruthenium complex

A simple and efficient pH-induced molecular “on/off” switching has been devised based on a symmetric bridged ruthenium dimer, [(edta)Ru(μ-Lb)Ru(edta)]n− (where n=4 or 3; Lb=benzotriazolate or 2H-benzotriazole; edta=ethylenediaminetetraacetate), by exploiting its unusual mixed-valence state behavior as a function of the pH. The intervalence transfer (IT) related phenomena have been rationalized in the light of the Mulliken–Hush formalism. Depending on the proton concentration, the electronic coupling and delocalization can be modulated to induce class III (deprotonated bridging ligand), class II (protonated), or even an intermediate borderline class II/class III system features.