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

• Two new Zn-based coordination complexes were synthesized, and showed excellent fluorescence properties. • Complexes 1 and 2 exhibit high sensitivity and selectivity for Cu 2+ sensing in aqueous solution. • Complexes 1 and 2 show different sensing mechanism to Cu 2+ . A great quantity of materials for the detection of Cu 2+ 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, [Zn 2 (L)(phen)(H 2 O) 3 •2.4H 2 O] n ( 1 ) and {[Zn(2,2′-bpy)(H 2 O) 4 ][Zn(H 2 L) 2 (2,2′-bpy)(H 2 O) 2 ]•H 2 O} ( 2 ), have been successfully constructed under hydrothermal conditions by using the H 4 L linker (3,5-di(3,4-dicarboxylphenyl) pyridine), N-auxiliary ligands (phen = 1,10-phenanthroline and 2,2′-bpy = 2,2′-bipyridine), and Zn 2+ with d 10 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 Cu 2+ 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 Cu 2+ . 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