Assembly of four new cobalt coordination polymers modulated by N-coligands: sensitive and selective sensing of nitroaromatics, Fe3+ and Cr2O72− in water

Abstract

Four new Co coordination polymers (CPs), formulated as [Co(L)(phen)] (1, 1D), [Co₃(L)₃(phen)₂·4H₂O] (2, 2D), [Co₃(L)₃(2,2′-bipy)₂·8H₂O] (3, 2D) and [Co₂(L)₃(4,4′-bipy)₂·] (4, 3D) (H₂L = 6-methoxy-2,2′-sulfone-4,4′-dicarboxylic acid, phen = 1,10-phenanthroline, 2,2′-bipy = 2,2′-bipyridine, 4,4′-bipy = 4,4′-bipyridine), have been solvothermally synthesized based on a functional dicarboxylate bridging ligand in the presence of various N-coligands. Complex 1 features a 3D supramolecular architecture composed of parallel linear chains assembled via π–π interactions. Complexes 2 and 3 have similar structures, which are both (4,4)-connected 2D networks possessing 1D channels based on linear trinuclear [Zn₃(CO₂)₆N₄] clusters. Complex 4 contains (4,4)-connected 2D layers based on binuclear clusters, which are further linked into a 3D pillar-layered framework by 4,4′-bipy. Luminescence studies indicate that 2 and 3 both show strong fluorescence and good stability in water, and they can be used as multi-responsive sensors for selective sensing of nitroaromatics, Fe³⁺ and Cr₂O₇²⁻ in water via luminescence quenching with fast response. Remarkably, 2 and 3 can be conveniently regenerated for at least four times without sacrificing their quenching efficiencies. The possible mechanisms for the luminescence quenching have been investigated in detail.