The Dependence of Ligand to Metal Charge Transfer Oscillator Strength on the Nature of the Ruthenium (III)-Cyanamide Bond: Outersphere Perturbations

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Abstract
The extent of electronic coupling between donor and acceptor wave-functions can play a dominant role in determining the rate of electron transfer. This is particularly true for biological electron transfer systems in which the redox sites are far apart or linked by a bridging ligand. In this study, we have investigated the extent to which electronic coupling between Ru(III) and an an — ionic phenylcyanamide ligand as measured by the b1* ← b1 LMCT oscillator strength is affected by the nature of the outer coordination sphere. The LMCT oscillator strength was found to decrease with increasing solvent donor number. We suggest that the trend in oscillator strength can largely be rationalized in terms of the magnitude of the π overlap between Ru(III) and cyanamide anion group. When the cyanamide anion group is incorporated into the bridging ligand of a Ru(III, II) mixed—valence complex, the oscillator strength of the resulting LMCT band will be a probe of the extent to which the acceptor wavefunction is coupled to the bridging ligand. By varying solvent donor properties, it will be possible to tune this interaction and observe this effect on the coupling between ruthenium ions as measured by the intervalence transition.

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