Highly Selective Ratiometric Sensors for Pb2+ 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 Pb2+ in water constitutes an active area of research that impacts analytical, environmental, and inorganic chemistry. Herein, two novel water-stable 2D Zn-coordination polymers {[Zn2(H2O)2(tdc)2(bpy)]·(H2O)}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 (Ca2+, Mg2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+ Cd2+, Hg2+ and Pb2+) 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 Cu2+, Cd2+ and Hg2+ in the micromolar concentration range (detection limit = 1.78 ± 10 μM). Such selectivity/affinity of Pb2+ over Hg2+ for luminescent chemosensors is still rare. On the basis of spectroscopic tools (1H 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 Pb2+ ions. The use of flexible luminescent Zn-coordination polymers as sensors for selective and direct detection of Pb2+ in aqueous media has been unexplored until now.

Recent advances in structures and applications of coordination polymers based on cyclohexanepolycarboxylate ligands

Coordination polymers (CPs) are emerging crystalline materials constructed by metal entities and organic ligands through coordination bonds, containing infinite coordination units in one, two, or three dimensions. Here an overview...

Efficient chemosensors for toxic pollutants based on photoluminescent Zn(ii) and Cd(ii) metal-organic networks

Optical sensors with high sensitivity and selectivity, as important analytical tools for chemical and environmental research, can be realized by straightforward synthesis of luminescent one-, two- and three-dimensional Zn(ii) and Cd(ii) crystalline coordination arrays (CPs and MOFs). In these materials with emission centers typically based on charge transfer and intraligand emissions, the quantitative detection of specific analytes, as pesticides or anions, is probed by monitoring real-time changes in their photoluminescence and color emission properties. Pesticides/herbicides have extensive uses in agriculture and household applications. Also, a large amount of metal salts of cyanide is widely used in several industrial processes such as mining and plastic manufacturing. Acute or chronic exposure to these compounds can produce high levels of toxicity in humans, animals and plants. Due to environmental concerns associated with the accumulation of these noxious species in food products and water supplies, there is an urgent and growing need to develop direct, fast, accurate and low-cost sensing methodologies. In this critical frontier, we discuss the effective strategies, chemical stability, luminescence properties, sensitivity and selectivity of recently developed hybrid Zn(ii)/Cd(ii)-organic materials with analytical applications in the direct sensing of pesticides, herbicides and cyanide ions in the aqueous phase and organic solvents.

Structure of a Luminescent MOF-2 Derivative with a Core of Zn(II)-Terephthalate-Isoquinoline and Its Application in Sensing of Xylenes

A new blue photoluminescent 2D metal–organic framework, 1, with formula {[Zn2(μ2-BDC)2(iQ)2]}∞ has been synthesized in a high yield under solvothermal conditions by reacting Zn(II) ions with 1,4-benzenedicarboxylic acid (H2BDC) and isoquinoline (iQ) in DMF. Compound 1 was thoroughly characterized by single-crystal X-ray diffraction, solid-state cross-polarization magic-angle spinning 13C NMR, X-ray powder diffraction, scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), and thermoanalysis. The crystal structure of 1 showed interpenetrated 2D frameworks consisting of dinuclear paddle-wheel cores Zn2; moreover, this material possessed thermostability up to 310 °C. The CPMAS 13C-NMR spectrum of 1 is consistent with the symmetry of the crystal structure. Luminescence studies showed that 1 strongly enhances its fluorescence emission in the presence of xylene isomers with a pronounced selectivity to p-xylene.

Dinuclear complexes of Mn, Co, Zn and Cd assembled with 1,4-cyclohexanedicarboxylate: synthesis, crystal structures and acetonitrile fluorescence sensing properties

Selective and reversible fluorescence sensing of acetonitrile in water by [Cd₂(H₂O)₂(chdc)₂(bipy)₂]·H₂O with a detection limit of 1.1 × 10⁻⁶ M.

A sensitive photoluminescent chemosensor for cyanide in water based on a zinc coordination polymer bearing ditert-butyl-bipyridine

Sensitive and direct sensing of cyanide in buffered aqueous solutions at pH = 7.0 by three new blue photoluminescent zinc-1,4-cyclohexanedicarboxylato coordination polymers bearing di-alkyl-2,2′-bipyridines has been achieved.