A Trinuclear Zinc Coordination Cluster Exhibiting Fluorescence, Colorimetric Sensitivity, and Recycling of Silver Ion and Detection of Cupric Ion

The detection and reusage of transition-metal ions play a crucial role in human health and environmental protection. Recently, various analytical methods and substances have been successfully applied to probe or sense silver ions; however, rare representative examples have been presented regarding the simultaneous detection of silver and silver recycling with the elemental silver powder form. Herein, an unparalleled sensing mechanism for silver ions and recycling silver in its elemental form is exemplified by a fluorescent trinuclear zinc coordination cluster possessing the dual function of colorimetric sensing of silver and responding cupric ions. A Schiff-base-based trinuclear zinc coordination cluster, 1, with formula Zn3(L1)2(CH3COO)2(H2O)2, has been successfully synthesized by the initial exploration of multidentate ligand H2L1-((E)-2,4-di-tert-butyl-6-((2-hydroxy-3-methoxybenzy-lidene)amino)phenol) with various metal ions under self-assembly reactions. Complex 1 is highly fluorescent in solution and as a solid, in addition to acting as a fluorescence sensor toward AgI in ethanol media. Compound 1 displays distinctive sensing of AgI through the fluorescence quenching effect at 576 nm and signal augment at 446 nm over 11 kinds of cations in the absence of interference. The proposed sensing mechanism is attributed to the ligands in 1 which interact with AgI; the ligands undergo oxidation cyclization reaction, leading to the formation of 2 with the formula Zn3(L2)4(CH3COO)2·2CH3CH2OH·H2O, and AgI reduction to elemental Ag powder. Compound 1 presents specific selectivity and sensitivity for AgI in ethanolic solution with a detection limit of 0.1722 μM. The orange color of 1 changes to colorless during the mixing of a small amount of AgI, revealing its potential practical application in naked-eye detection of AgI. Furthermore, 2 exhibits obvious fluorescence emission at 448 nm (λex = 380 nm) and selectively responds to CuII over 11 kinds of metal ions with the fluorescence "turn-off" owing to the formation of 3 in ethanolic solution; it also has a detection limit of 0.0226 μM.