EXAMINATION OF CONDITIONS UNDER WHICH THE REDUCTION OF THE COBALTOCENIUM CATION CAN BE USED AS A STANDARD VOLTAMMETRIC REFERENCE PROCESS IN ORGANIC AND AQUEOUS SOLVENTS

The two one-electron processes for reduction of the cobaltocenium cation as the hexafluorophosphate salt have been studied extensively in both aprotic and protic solvents at a hanging mercury drop electrode and at conventionally and microsized platinum, gold, and glassy carbon disk electrodes of various radii. Under carefully chosen conditions, both the Cc+/Cc0 and Cc0/Cc- couples (Cc = cobaltocene) can be used as reversible voltammetric reference systems. However, the Cc+/Cc0 couple is the preferred reference process since the combination of a very negative potential and possible overlap problems with the solvent response sometimes prevents the Cc0/Cc- couple from being used as a practical voltammetric reference system. Furthermore, the half-wave potential for the Cc+/Cc0 system was calculated to be -1.35 +/- 0.01 V vs the widely used Fc+/Fc reference couple (Fc = ferrocene) and is essentially independent of electrode material, electrolyte, and solvent relative to the ferrocene reference potential. In contrast,the half-wave potential for the Cc0/Cc- couple relative to the ferrocene reference potential is significantly dependent on the nature of the solvent.