Ruthenium, standard reduction potentials

Table 25.2 Standard reduction potentials for iron, ruthenium and osmium in acidic aqueous solution...

Passage of 1.0 mol of electrons (one faraday, 96,485 A s) will produce 1.0 mol of oxidation or reduction—in this case, 1.0 mol of Cl- converted to 0.5 mol of Cl2, and 1.0 mol of water reduced to 1.0 mol of OH- plus 0.5 mol of H2. Thermodynamically, the electrical potential required to do this is given by the difference in standard electrode potentials (Chapter 15 and Appendix D) for the anode and cathode processes, but there is also an additional voltage or overpotential that originates in kinetic barriers within these multistep gas-evolving electrode processes. The overpotential can be minimized by catalyzing the electrode reactions in the case of chlorine evolution, this can be done by coating the anode with ruthenium dioxide. 

Electrochemical properties such as redox potential can also serve as inputs to molecular YES logic gates since redox indicators also have a rather long history. " Complex 2 is poorly emissive at 610 nm (when excited at 453 nm) as a result of PET from the ruthenium-based lumophore to the benzoquinone moiety across the dimethylene spacer. If a potential of —0.6 V (vs standard calomel electrode SCE) is applied to it in wet acetonitrile, the benzoquinone unit is fully reduced to the hydroquinone form once two coulombs are passed per equivalent of 2. This succeeds because the reduction potential of 2 is —0.44 V. Upon reduction, a luminescence enhancement factor of 6 is seen. The system is stable in both the benzoquinone and hydroqninone forms in the absence of applied potentials, which means that these cases show evidence of memory unlike ion-driven cases such as 1. However, the hydroquinone form can be reset to 2 by application of two coulombs at a potential of -1-1.1 V. 

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