Co(II) and Cd(II) Metal–Organic Frameworks as Bifunctional Fluorescent Probes for Targeted Detection of Fe(III) and Cr(VI)

Abstract Two novel metal–organic frameworks (MOFs), [Cd(L)(BPDC)(H 2 O)]·DMA ( 1 ) and [Co(L)(BPDC)(H 2 O)]·2H 2 O ( 2 ), were solvothermally synthesized using 3,3′‐bis(1H‐imidazol‐1‐yl)biphenyl (L) and biphenyl‐4,4′‐dicarboxylic acid (H 2 BPDC) as mixed ligands, with Cd(NO 3 ) 2 ·4H 2 O and Co(NO 3 ) 2 ·6H 2 O as metal sources, respectively. 1 is characterized by a theoretically porous three‐dimensional framework, whereas 2 is constructed as a three‐dimensional supramolecular framework. A significant influence of the distinct coordination geometries of the metal centers on the structural architectures was observed, as evidenced by the unique configurations of the Cd/Co‐MOFs. Reliable thermal stability was demonstrated for both 1 and 2 by thermal stability tests. The fluorescent properties of 1 were investigated in depth, and its capability for accurate recognition of Fe 3+ , CrO 4 2− , and Cr 2 O 7 2− in aqueous solution through fluorescence turn‐off response was revealed. High sensitivity and a low detection limit were exhibited by this recognition system, suggesting that 1 can be considered a potential identification tool for the detection of heavy metal contaminants in aqueous environments. UV–vis spectroscopy indicates that competitive absorption is the primary cause of variation in the fluorescence signal.