Stepwise Coordination Followed by Oxidation Mechanism for the Multichannel Detection of Cu2+ in an Aqueous Environment

The cyclometalated ruthenium-dipicolylamine (DPA) derivative 3(PF6) has been synthesized. In the presence of 1 equiv of Cu2+ in an aqueous environment, a new redox peak at -0.03 V vs Ag/AgCl appeared. This peak is assigned to the Cu-II/1 process as a result of the complexation of Cu2+ with the DPA unit. In the presence of 2 equiv of Cu2+, the metal-to-ligand charge-transfer absorption of 3(PF6) at 516 nm significantly decreased and a new absorption peak at 750 nm appeared. Accordingly, the solution turned from purple to yellow. The new absorption at 750 nm is assigned to the ligand-to-metal charge-transfer absorption, as a result of the oxidation of the ruthenium component by Cu2+. These optical and electrochemical changes have not been observed in the presence of the other 13 metal ions examined. A single-crystal X-ray structure of 3 center dot Cu center dot CH3CN center dot 3ClO(4) has been obtained and used for the elucidation of the stepwise recognition mechanism (coordination followed by oxidation), together with the electrochemical and spectroscopic studies of the two model compounds 2(PF6) and 4 with only the ruthenium component or the DPA unit.