Sulphur-rich functionalized calix[4]arenes for selective complexation of Hg²⁺over Cu²⁺, Zn²⁺and Cd²⁺

Abstract

The syntheses of two new ligands based on a calix[4]arene scaffold in the cone conformation functionalized on the phenolic positions 1 and 3 by diethylthiophosphonates (L1) or tetra(tri)thioethyleneglycol (L2) crowns are described. Together with ligand L3, the parent calix[4]arene substituted by a penta(tetra)thioethyleneglycol crown, the spectroscopic properties of the ligands were determined by means of UV-Vis absorption spectroscopy and steady-state and time-resolved fluorescence spectroscopy, showing that the ligands display modest but non-negligible intrinsic fluorescence properties (ϕ = 0.023; 0.026 and 0.029 for L1, L2 and L3 in CHCl, respectively). The X-ray crystal structures of ligand L1, and of its synthetic precursor were determined and analyzed for their capacity to accommodate the incoming cationic species. The ligands were further investigated for their complexation properties of divalent cations such as Cu, Zn, Hg and Cd (under their nitrate salts) in 1 : 1 CHCN/CHCl solutions (I = 0.01 M EtNNO, T = 25.0(2) °C), in which the additions of cations were monitored by absorption and steady-state fluorescence spectrophotometries. The stoichiometries of the corresponding complexes were assessed by ESI-MS, while insights into the structures of the complexes in solution were obtained with density functional theory (DFT) calculations. The influence of the sulphur and phenol coordinating moieties was addressed to show that the thiocrown compounds L2 and L3 displayed a marked affinity towards the soft mercuric cation (Δlog K ≥ 2), with no particular size selectivity effect, whereas ligand L1 can accommodate both the thio and phenol units to coordinate with Cu(ii). Altogether, these results point to the use of L3 as a selective fluoroionophore for detection of Hg.

Thioether-Crown-Rich Calix[4]arene Porous Polymer for Highly Efficient Removal of Mercury from Water

“… Prior to polymerization, both the monomer and linker were synthesized in good yields by following reported procedures with relevant modifications (details in the Supporting Information). , The insoluble polymer product was centrifuged and washed multiple times with various solvents including THF, acetone, CHCl 3 , DMF, and DMA. In the FTIR spectrum of S-CX4P , the absence of terminal alkyne −C–H stretching absorption bands near 3300 cm –1 that are present in the spectrum of 2 (Figure S1) and the presence of peaks near 2230, 2920, and 3350 cm –1 , which correspond to alkyne CC stretching vibrations, −C–S–C– vibrations from thioether crown and calix[4]­arene −O–H stretching vibrations, respectively, confirm successful cross-coupling.…”

“…Calix­[4]­arenes are polyaromatic, hydrophobic, macrocyclic structures − with excellent preorganized binding moieties for biphasic extraction and purification of Hg from aqueous phases as previously demonstrated. , Mercury being a soft Lewis acid, equipping the calixarenes with soft base binding moieties, such as thioethers, yields monomers with additional capacity for Hg removal. A recent study demonstrated that sulfur and phenol-coordinating moieties in a thia-crown derivative of calix[4]­arene enhance the macrocycle’s affinity for soft mercuric cations (Δlog K ≥ 2) . Here, we rationally selected a calix[4]­arene derivative with a thioether-crown unit specific for Hg binding as a functional monomer to synthesize a novel covalent porous polymer ( S-CX4P ).…”

“…A recent study demonstrated that sulfur and phenol-coordinating moieties in a thia-crown derivative of calix [4]arene enhance the macrocycle's affinity for soft mercuric cations (Δlog K ≥ 2). 31 Here, we rationally selected a calix [4]arene derivative with a thioether-crown unit specific for Hg binding as a functional monomer to synthesize a novel covalent porous polymer (S-CX4P). The calix [4]arene backbone provides rigidity to the thioether-crown unit, which ensures strong metal coordination and maintains overall network porosity allowing easy accessibility to the sulfur atoms homogeneously distributed in the polymer.…”

1,4-Bis(2-(pyridin-4-yl)vinyl)naphthalene and Its Zinc(II) Coordination Polymers: Synthesis, Structural Characterization, and Selective Luminescent Sensing of Mercury(II) Ion

“…In recent years, luminescent coordination polymers (CPs) have attracted much attention owing to their designable architectures, robust thermal stability, and various chemical and physical properties. − The molar ratios of reactants, pH values, solvent systems, counterions, templates, and reaction temperatures and so on could impose effects on the final structures of the resulting CPs. − Moreover, the fluorescent properties of CPs are tunable through modifying organic ligands, metal ions/cluster units, and even the CPs structures. , Up to now, various CPs have been synthesized as effective luminescent probes for detecting inorganic and/or organic cations, anions, and neutral molecules. − Many pyridine-appended π-conjugated derivatives have proven to be as efficient sensing fluorophores for metal ions and the π-conjugated groups may impose their selectivity and sensitivity. − For example, the ligand 1,4-bis­[2-(4-pyridyl)­ethenyl]­benzene (bpeb) with a longer π-conjugated spacer (CC−C 6 H 4 –CC) showed higher selectivity and sensitivity for detecting Hg 2+ than the ligand di­(4-pyridyl)­ethylene with a shorter π-conjugated spacer (CC) . However, compared with organic probes, − the CP-based sensors for probing Hg 2+ are quite limited in numbers. − Can expanding the π-conjugation of the aforementioned ligand bpeb increase the selectivity and sensitivity for sensing Hg 2+ ? With this question in mind, we delicately chose and prepared a bpeb analogue, 1,4-bis­(2-(pyridin-4-yl)­vinyl)­naphthalene (1,4-bpyvna), in which a larger π-conjugated naphthalene group replaces the central phenyl group in bpeb.…”