Anion Extraction Properties of a New “Proton-Switchable” Terpyridin-Conjugated Calix[4]arene

Supramolecular chemistry of liquid-liquid extraction

Liquid-Liquid Extraction (LLE) is a venerable and widely used method for the separation of a targeted solute between two immiscible liquids. In recent years, this method has gained popularity in the supramolecular chemistry community due to the development of various types of synthetic receptors that effectively and selectively bind specific guests in an aqueous medium through different supramolecular interactions. This has eventually led to the development of state-of-the-art extraction technologies for the removal and purification of anions, cations, ion pairs, and small molecules from one liquid phase to another liquid phase, which is an industrially viable method. The focus of this perspective is to furnish a vivid picture of the current understanding of supramolecular interaction-based LLE chemistry. This will not only help to improve separation technology in the chemical, mining, nuclear waste treatment, and medicinal chemistry sectors but is also useful to address the purity issue of the extractable species, which is otherwise difficult. Thus, up-to-date knowledge on this subject will eventually provide opportunities to develop large-scale waste remediation processes and metallurgy applications that can address important real-life problems.

Interfacial Self-Assembly of Organized Ultrathin Films of Tripodal Metal-Terpyridyl Coordination Polymers as Luminophores and Heterogeneous Catalysts for Photocatalytic CO2 Reduction

Metal-directed interfacial self-assembly of well-defined coordination polymer (CP) ultrathin films can control the metal complex arrangement and distribution at the molecular level, providing a convenient route for the design and fabrication of novel opto-electrical devices and heterogeneous catalysts. Here, we report the assembly of two series of CP multilayers with the transition-metal ions of Fe²⁺, Co²⁺, Zn²⁺ and Tb³⁺ as connectors and tripodal terpyridyl ligands of 4,4',4″-(1,3,5-triazine-2,4,6-triyl)tris(1-(4-([2,2':6',2″-terpyridin]-4'-yl)benzyl)pyridin-1-ium) (TerPyTa) and 4,4',4″-(benzene-1,3,5-triyl)tris(1-(4-([2,2':6',2″-terpyridin]-4'-yl)benzyl)pyridin-1-ium) (TerPyBen) as linkers at the air-water interface. The as-prepared Langmuir-Blodgett (LB) films display strong luminescence, with the emission wavelength and relative intensity dependent on both the metal ions and linkers; among them, the Zn-TerPyTa and Zn-TerPyBen CPs give off the strongest luminescent emission centered at about 370 nm with an emission lifetime of approximately 0.2-0.3 ns. The Tb-TerPyTa CPs can give off emission at approximately 490, 546, 586, and 622 nm, attributed to the ⁵D₄ to ⁷F_3-6 electron transitions of typical Tb³⁺ ions. Finally, these CP LB films can act as efficient heterogeneous photocatalysts for the CO₂ reduction to selectively produce CO. The catalytic efficiency can be optimized by adjusting the experimental conditions (light sensitizer, electron donor, and water content) and CP composition (metal ion and ligand) with an excellent yield of up to 248.1 mmol g^-1. In particular, it is revealed that, under the same conditions, the catalytic efficiency of the Fe-TerPyTa CP LB film is nearly 2 to 3 orders of magnitude higher than that of the other metalated complexes investigated in the homogeneous system. UV-vis spectroscopy and cyclic voltammetry studies demonstrated that the dual active sites of Fe-terpyridine and TerPyTa units contribute to the enhanced catalytic activity. This work provides an effective method to introduce the earth-abundant metal complexes into CP films to construct efficient noble-metal-free photocatalysts for the CO₂ reduction.

Synthesis of new anthracene-substituted calix[4]triazacrown-5 as highly sensitive fluorescent chemosensor and extractant against hazardous dichromate anion

A new fluorogenic anthracene functionalized calix[4]triazacrown-5 (Ant-AzClx) was successfully synthesized using a simple Schiff's base reaction. The ¹ H-NMR, ¹³ C-NMR, ESI-MS, and elemental analysis techniques were performed to characterize its structure. Excited at 370 nm, Ant-AzClx reveals excimer emission at 418 nm. Therefore, its anion binding properties were investigated against F^- , HCO₃ ^- , H₂ PO₄ ^- , NO₃ ^- , Cr₂ O₇ ^2- , and SO₄ ^2- ions. When hazardous dichromate anion was introduced into medium, the fluorescence intensity of Ant-AzClx was markedly quenched. The binding constant, stoichiometry, the detection limits and Stern-Volmer equation for the complex formed between Ant-AzClx and Cr₂ O₇ ^2- ion were determined. Furthermore, the ¹ H-NMR technique was also performed to assess the mechanism of the complex (Ant-AzClx@Cr₂ O₇ ^2- ). Apart from its excellent fluorescent chemosensor properties for selective and sensitive recognition of Cr₂ O₇ ^2- ion, Ant-AzClx was used as an efficient extractant towards dichromate anion. The extraction results indicated that Ant-AzClx exhibited high extraction capability, leading to it being a promising extractant for the removal of dichromate anions from water.

Microwave-Assisted Synthesis of Bidentate Chiral Unsymmetrical Urea Derivatives of P-tert-butylcalix[4]Arene and their Anion Recognition Properties

Four new derivatives of p-t-butylcalix[4]arene containing two (1,3-distal) chiral unsymmetrical urea moieties at the lower rim were synthesised in four steps. Their anion recognition properties toward MeCO2−, H2PO4−, NO3−, I−, Br−, Cl− were assessed by UV-Vis titration spectroscopy. All the receptors showed the strongest recognition ability for MeCO2−, one of them having an association constant of 3139 M-1. 1H NMR studies of this receptor complex confirmed its tight binding of MeCO2−.