Structural distinction and highly sensitive fluorescent detection properties of Cd-based multifunctional sensors with three flexible isomers

Many environmental pollutants are found and need to be detected and treated with the rapid development of industry. Three novel Cd (II) coordination polymers (Cd-CPs) (1–3), with the formula of [Cd(2-HDBB)(4,4′-bbpy)](1), [Cd(3-HDBB)(4,4′-bbpy)](2) and [Cd(4-HDBB)(4,4′-bbpy)_0.5·2H₂O](3) based on three soft organic isomers: n-(3,5-dicarboxylato benzyloxy) benzoic acid (n = 2, 3 or 4-H₃DBB), with one linear N-donor ligand 4,4′-bis(imidazolyl) biphenyl (4,4′-bbpy) have been synthesized hydrothermally and characterized in detail. The significant structural differences are both coordination polymers 1 and 2 featuring two-dimensional networks, while 3 with 1D ladder-like chain due to the change of isomers. Despite structural differences, the series of Cd-CPs exhibits similar fluorescence sensing properties. Fluorescent sensing properties exhibit all the Cd-CPs have been discovered to detect Fe³⁺, Cr₂O₇²⁻, tetracycline (TET) and nitrobenzene (NB) selectively and sensitively with the low detection limits, respectively. The results of theoretical calculation verified the fluorescence detection mechanism of NB by these cadmium complexes. Therefore, the Cd-CPs might be used as an excellent multi-functional luminescent sensor in the future.