FIGURE 4. The electrochemical behaviour of the synthetic H-cluster model.

a, Cyclic voltammogram of D (0.1 M [NBu₄][BF₄]-MeCN, 30 mV s^-1, vitreous carbon), showing interconverting redox processes I and II. E_1/2 for II occurs at a potential close to that for C, indicative of the rearrangement of the -S bonded subsite to the terminal alkylthiolate. Inset, first-scan response at the faster scan rate of 0.1 V s^-1 but otherwise under the same conditions; note suppression of the interconversion. b, Cyclic voltammogram of D (1.5 mM), showing the electrocatalytic response in the absence (trace i) and in the presence (trace ii) of 4,6-dimethyl pyridinium cation as a source of protons (15 mM) at a normalized scan rate of 0.1 V s^-1. The peak current for proton reduction in the absence of the catalyst is within 5% of that in its presence, but is shifted about 200 mV to a more negative potential.