Highly Selective Ratiometric Sensors for Pb2+ Based on Luminescent Zn(II)-Coordination Polymers with Thiophenedicarboxylate. Crystal Structures and Spectroscopic Studies

Abstract

The development of luminescent coordination polymers for the selective sensing of Pb 2+ in water constitutes an active area of research that impacts analytical, environmental, and inorganic chemistry. Herein, two novel water-stable 2D Zn-coordination polymers {[Zn 2 (H 2 O) 2 (tdc) 2 (bpy)]·(H 2 O)} n 1 and [Zn(tdc)(tmb)] n 2 (tdc = thiophenedicarboxylate; bpy = 4,4’-bipyridine and tmb = 4,4'-trimethylenebipyridine) were synthesized, structurally determined by single crystal X-ray diffraction, and studied in-depth as luminescent sensors for a series of cations (Ca 2+ , Mg 2+ , Mn 2+ , Fe 2+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ Cd 2+ , Hg 2+ and Pb 2+ ) in 20% aqueous ethanol. These Zn-polymers possess photostability in 20% aqueous ethanol with a strong emission at 410 upon excitation at 330 nm and quantum yields of around Φ = 0.09. Under these conditions, Pb +2 can be efficiently sensed with polymer 2 through a fluorescent ratiometric response with selectivity over common interfering metal ions such as Cu 2+ , Cd 2+ and Hg 2+ in the micromolar concentration range (detection limit = 1.78 ± 10 μM). Such selectivity/affinity of Pb 2+ over Hg 2+ for luminescent chemosensors is still rare. On the basis of spectroscopic tools ( 1 H NMR, far ATR-IR, PXRD), the X-ray crystal structure of 2 , and Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopic analysis, the ratiometric fluorescent response is proposed via an efficient metal-ion exchange driven through interactions between thiophenedicarboxylate rings and Pb 2+ ions. The use of flexible luminescent Zn-coordination polymers as sensors for selective and direct detection of Pb 2+ in aqueous media has been unexplored until now. Graphical Abstract

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