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

The development of luminescent coordination polymers for the selective sensing of Pb 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(HO)(tdc)(bpy)]·(HO)} 1 and [Zn(tdc)(tmb)] 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, Mg, Mn, Fe, Co, Ni, Cu, Zn Cd, Hg and Pb) 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 can be efficiently sensed with polymer 2 through a fluorescent ratiometric response with selectivity over common interfering metal ions such as Cu, Cd and Hg in the micromolar concentration range (detection limit = 1.78 ± 10 μM). Such selectivity/affinity of Pb over Hg for luminescent chemosensors is still rare. On the basis of spectroscopic tools (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 ions. The use of flexible luminescent Zn-coordination polymers as sensors for selective and direct detection of Pb in aqueous media has been unexplored until now.