Two luminescent Zn(II) coordination complexes as fluorescence-responsive sensors for efficient detection of Cu2+ ions

Abstract

A great quantity of materials for the detection of Cu2+ have been reported, but the structural transformation of these materials is difficult to understand during the detection process and hence less reported. Here, two new Zn-based complexes, namely, [Zn2(L)(phen)(H2O)3·2.4H2O]n (1) and {[Zn(2,2′-bpy)(H2O)4][Zn(H2L)2(2,2′-bpy)(H2O)2]·H2O} (2), have been successfully constructed under hydrothermal conditions by using the H4L linker (3,5-di(3,4-dicarboxylphenyl) pyridine), N-auxiliary ligands (phen = 1,10-phenanthroline and 2,2′-bpy = 2,2′-bipyridine), and Zn2+ with d10 electron configuration. X-ray crystallographic analysis suggests that 1 features a 2D layer, which is further extend into a 3D supramolecular structure by hydrogen bonding interactions. 2 displays a 0D ionic structure, which can form 2D framework via hydrogen bonding. Notably, complexes 1 and 2 contain multiple O functional sites that can be used to detect guest metal ions. As expected, photoluminescence studies reveal that complexes 1 and 2 are promising luminescence sensors for selective detection of trace amounts Cu2+ ions in aqueous solutions by luminescence quenching mechanism, featuring high sensitivity, and low detection limits (74.6 nM and 301.7 nM). Complexes 1 and 2 have different sensing mechanisms for Cu2+. The quenching mechanism of complex 2 is rare, that is, the irreversible exchange of metal ions induces crystal structural transformation and the exchange process can be clearly monitored by visual color changes