Nickel-Electrode-Confined {Ru(bipyrazine)₃[Fe(CN)₅]_n}^2–3n: An Inorganic Structural Matrix Yielding Photoinduced Multinuclear Charge-Transfer Reactivity

The complex {Ru(bpz)₃[Fe(CN)₅]_n}^2–3n (where n = 1–6 and bpz bipyrazine) containing a central ruthenium(II) and an overall octahedral site symmetry can be surface-attached to a variety of electrodes via reaction with electrogenerated nickel ions. The well-defined geometry of this complex allows it to be considered as a “molecular building block” for the construction of microstructure-specific chemically derivatized interfaces. In addition to exhibiting a sophisticated interfacial structure, this class of electrodes is found to yield both photocathodic and photoanodic currents under illumination in an aqueous electrolyte. The photocurrent is found to be molecular in nature and can be explained in terms of charge-transfer quenching of a Ru(II) → bpz charge-transfer excited state by the pendant pentacyanoferrate groups. Excitation and quenching events appear to be highly localized. The sense of the photocurrent is controlled by the initial oxidation state of the surface-confined iron. Under conditions yielding a photocathodic current, the charge is eventually consumed by the reduction of dissolved O₂.