Impact of confinement and interfaces on coordination chemistry: Using oxovanadate reactions and proton transfer reactions as probes in reverse micelles

The versatility of the heterogeneous environment in microemulsions and its impact on coordination chemistry is illustrated by the simple reactions of oxovanadates in aerosol-OT (AOT)/isooctane reverse micelles (RMs). In reverse micelles, vanadate dimerization at neutral and basic pH increases compared to bulk aqueous solution, consistent with localizing in the water pool and an increase in the proton concentration. Formation of tetrameric and pentameric oxovanadate also increases at neutral and basic pH in micellar environments, but at some pH values this system achieves oxovanadate mixtures not accessible in aqueous solutions. Proton transfer reactions monitored using decavanadate suggest that the interior of water pools have proton concentration approximating neutral pH values. These results lead to the proposal that a proton gradient from the RM interior toward the periphery is established in these systems, when the initial aqueous solution is acidic prior to RM formation. In addition to solvation, the effect of these RM structures on such simple systems (although less conventional coordination complexes), suggest the potential for application of these systems to direct the coordination chemistry of metals and metal complexes for preparative purposes. For example, in the emerging field of nanochemistry RMs are used as a template for the synthesis of nanostructures.