The ability to systematically alter the degree of coupling between two redox-active groups via the molecular bridge is of great theoretical and practical importance. Here, we describe the synthesis and characterization of a series of metal bis-alkynyl complexes of the form [FeIII(MAC)(C2R)2]+ (R = redox-active group), where MAC represents either a tetraamine or tetraimine supporting macrocycle. The mixed-valent species (i.e. [FeIII(MAC)(C2R)(C2R1+)]2+) are then addressed via IR and vis-NIR spectroelectrochemistry. Although the immediate bridging unit is the same in all cases (-C2-FeIII-C2-), the degree of saturation of the macrocycle is shown to have a profound effect on the efficiency of the electronic coupling in the single-electron oxidized states. Thus, the secondary ligand may be viewed as a synthetic handle to control coupling, changing the nature of the bridge from insulating to conducting. Moreover, with R = ferrocenyl, the first definitive use of a 3d transition metal “dopant” for enhancing coupling over the analogous organic (butadiynyl) bridge is reported, to the best of the authors’ knowledge.

Control of charge (de)localization in FeIII-based mixed-valent complexes via macrocyclic substitution

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