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 CuII/I 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·Cu·CH3CN·3ClO4 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.环金属化钌-二吡啶甲基胺（dipicolylamine，简称DPA）衍生物3(PF6)已成功合成。在水环境中存在1当量Cu²+时，出现了一处相对于Ag/AgCl参比电极位于-0.03 V的新氧化还原峰，该峰归属为Cu²+与DPA单元配位后产生的Cu(II)/Cu(I)氧化还原过程。当体系中存在2当量Cu²+时，3(PF6)在516 nm处的金属-配体电荷转移（metal-to-ligand charge transfer, MLCT）吸收峰显著减弱，并在750 nm处出现新的吸收峰；相应地，溶液由紫色变为黄色。750 nm处的新吸收峰归属为配体-金属电荷转移（ligand-to-metal charge transfer, LMCT）吸收，其源于Cu²+对钌组分的氧化作用。在其余13种被测试的金属离子存在时，均未观察到此类光学与电化学变化。本研究已获得3·Cu·CH3CN·3ClO4的单晶X射线结构，并结合仅含钌组分的模型化合物2(PF6)与仅含DPA单元的模型化合物4的电化学及光谱学研究，阐明了该分步识别机制（先配位后氧化）。