Metal-Assembled, Resorcin[4]arene-Based Molecular Trimer for Efficient Removal of Toxic Dichromate Pollutants and Knoevenagel Condensation Reaction

Harnessing the Chemical Functionality of Metal-Organic Frameworks Toward Removal of Aqueous Pollutants

Wastewater treatment has been bestowed with a plethora of materials; among them, metal-organic frameworks (MOFs) are one such kind with exceptional properties. Besides their application in gas adsorption and storage, they are applied in many fields. In orientation toward wastewater treatment, MOFs have been and are being successfully employed to capture a variety of aqueous pollutants, including both organic and inorganic ones. This review sheds light on the postsynthetic modifications (PSMs) performed over MOFs to adsorb and degrade recalcitrant. Modifications performed on the metal nodes and the linkers have been explained with reference to some widely used chemical modifications like alkylation, amination, thiol addition, tandem modifications, and coordinate modifications. The boost in pollutant removal efficacy, reaction rate, adsorption capacity, and selectivity for the modified MOFs is highlighted. The rationale and the robustness of micromotor MOFs, i.e., MOFs with motor activity, and their potential application in the capture of toxic pollutants are also presented for readers. This review also discusses the challenges and future recommendations to be considered in performing PSM over a MOF concerning wastewater treatment.

Anion-Directed Self-Assembly of Calix[4]arene-Based Silver(I) Coordination Polymers and Photocatalytic Degradation of Organic Pollutants

Coordination polymers (CPs) have recently emerged as promising candidates for heterogeneous photocatalysis due to their structural designability and tunable properties. Herein, we developed two novel Ag(I)-calix[4]arene coordination polymers with the formula {[Ag₂(μ-NO₃)L¹]}_n (CP 1) and {[AgL¹]·PF₆}_n (CP 2) (L¹ = 2-mercapto-5-methyl-1,3,4-thiadiazole resorcinol calix[4]arene). Crystallography revealed that anion coordination and self-inclusion behavior induced the cavitand and silver ions to self-assemble into well-defined CPs 1 and 2 with different topological coordination frameworks, respectively. Furthermore, CPs 1 and 2 display high photocatalytic activity for the photodegradation of rhodamine B (RhB) and methyl orange (MO) in an aqueous solution under mild conditions (WLED and UV irradiation). The comparison results demonstrate that CP 1 exhibited better photocatalytic performance than CP 2, which correlated well with the differences in their molecular structure and HOMO-LUMO energy gaps. The photocatalysis products and possible intermediates were successfully monitored and determined using mass spectrum, gas chromatography, and electron paramagnetic resonance measurements. The rational photocatalysis mechanism was further investigated and proposed.

Sand-Based Economical Micro/Nanocomposite Materials for Diverse Applications

Sand is one of the most fundamental construction materials that is of significant importance and widely used for making concrete, plasters, and mortars, and also for filling under floor and basements. Sand-derived functional materials, for instance superhydrophobic sand, which can be used to prepare liquid marble, separate oil-water mixtures, and transport liquids, have recently been a highly topical and promising research field. However, such materials are mainly prepared using valuable surface modification agents via complicated procedures that are difficult for mass-production, which restricted their true applications. Here, we developed a simple, low-cost, and efficient method for the development of sand-based hierarchical micro/nanostructured composite materials with diverse applications. Briefly, micro/nanostructured superhydrophobic sand was synthesized by one-step in situ growth of a network layer of silicone nanofilaments on the surface of sand microparticles, using only one cheap chemical of small molecules of silanes. The as-prepared superhydrophobic sand displays excellent performance in waterproofing, water storage, soil moisturizing, and oil-water separation. Furthermore, sand-supported micro/nanocomposite catalysts were obtained through covalent attachment of polyamines on the surface of silicone nanofilaments. Such composites, packed in a glass column, were used as a simple flow reactor for Knoevenagel condensation reactions. Quantitative amounts of pure products without further purification can be obtained in such a simple way that just allowing the reactants solution flows through the composite catalysts driven by gravity. These results pave the way toward the development of sand-based multifunctional materials with great potential for industrial use, given their versatile functions and excellent performances but easy-to-fabricate, low-cost preparation procedure.

Metal-organic cages against toxic chemicals and pollutants

The continuous release of toxic chemicals and pollutants into the atmosphere and natural waters threatens, directly and indirectly, human health, the sustainability of the planet, and the future of society. Materials capable of capturing or chemically inactivating hazardous substances, which are harmful to humans and the environment, are critical in the modern age. Metal-organic cages (MOCs) show great promise as materials against harmful agents both in solution and in solid state. This Highlight features examples of MOCs that selectively encapsulate, adsorb, or remove from a medium noxious gases, toxic organophosphorus compounds, water pollutant oxoanions, and some emerging organic contaminants. Remarkably, the toxicity of interacting contaminants may be lowered by MOCs as well. Specific cases pertaining to the use of these cages for the chemical degradation of some harmful substances are presented. This Highlight thus aims to provide an overview of the possibilities of MOCs in this area and new methodological insights into their operation for enhancing their activity and the engineering of further remediation applications.

Assembly of cobalt-p-sulfonatothiacalix[4]arene frameworks with phosphate, phosphite and phenylphosphonate ligands

Three cobalt-calixarene coordination frameworks, namely, {[Co4Cl(H4TC4AS)]4(HPO3)8}4− (CIAC-253), {[Co4Cl(H4TC4AS)]4(PO4)8}12− (CIAC-254) and {[Co4Cl(H4TC4AS)]3(Ph-PO3)6}3− (CIAC-255) were obtained by solvothermal reaction of a cobalt salt, sodium p-sulfonatothiacalix[4]arene (Na4H4TC4AS) and phosphate, phosphite and phosphonate ligands. In CIAC-253 and CIAC-254, the shuttlecock-like Co4Cl-(TC4AS) secondary building units (SBUs) are bridged by HPO3 2− or PO4 3− anions into two quadrilateral frameworks while in CIAC-255, the Co4Cl-(TC4AS) SBUs are linked into a triangular framework by phenylphosphonate anions. The supramolecular interactions between the phenyl groups of phosphonate and TC4AS play a crucial role in the formation of the triangle. Magnetic measurements revealed that all the cobalt(II) centers exhibit antiferromagnetic interactions.

Triazole-directed fabrication of polyoxovanadate-based metal-organic frameworks as efficient multifunctional heterogeneous catalysts for the Knoevenagel condensation and oxidation of alcohols

By introducing 4-amino-1,2,4-triazole (4-NH2-trz), three new polyoxovanadate-based metal-organic frameworks (PMOFs) [Ni3(4-NH2-trz)6][V6O18]·3H2O (1), [Co3(4-NH2-trz)6][V6O18]·3H2O (2) and [Cu3OH(4-NH2-trz)3H2O][VO3]5·H2O (3) have been synthesized and thoroughly characterized by single-crystal X-ray diffraction (SXRD), powder X-ray diffraction (PXRD), infrared spectroscopy (FT-IR), thermogravimetric (TG) analysis and elemental analysis (EA). Among them, PMOFs 1 and 2 had similar structures containing [V6O18]6- clusters; however, PMOF 3 was isolated as a structure containing a [VO3]55- cluster when the amount of the 4-NH2-trz ligand was reduced to half with the other synthesis conditions being the same as those of PMOFs 1 and 2 except for the transition-metal chlorides. Furthermore, the negative charges of polyoxovanadate [V6O18]6- and [VO3]55- anions were balanced by trinuclear complex cations [Ni3(4-NH2-trz)6]6- for 1, [Co3(4-NH2-trz)6]6- for 2 and [Cu3OH(4-NH2-trz)3H2O]5- for 3, respectively. PMOFs 1-3 were further used as heterogeneous catalysts in the Knoevenagel condensation under solvent-free conditions and showed high catalytic activity. PMOF 1 showed moderate catalytic activities in the oxidation of various aromatic alcohols using H2O2 as an oxidant. Moreover, PMOF 1 could be reused at least three times without losing its activity.

Two new calix[4]resorcinarene-based coordination cages adjusted by metal ions for the Knoevenagel condensation reaction

Two new calix[4]resorcinarene-based coordination cages, namely, [Zn4(TPC4R)(PDC)4]·2DMF·6H2O (1-Zn) and [In11(TPC4R)2(PDC)16(μ2-OH)2(H2O)2]·[(CH3)2NH2]·8DMF·20H2O·EtOH (2-In), have been synthesized via solvothermal reactions (TPC4R = tetra(2-(4H-pyrazol-3-yl)pyridine)calix[4]resorcinarene, H2PDC = 3,5-pyridinedicarboxylic acid, DMF = N,N'-dimethylformamide). By carefully tuning different metal ions, two structurally different cages 1-Zn and 2-In were achieved. The former shows a bowl-shaped structure, while the latter features a dumbbell-like structure. After activation, they exhibited unsaturated Zn(ii) or In(iii) Lewis acid sites and the free nitrogen Lewis base sites of the PDC2-. Therefore, they were employed as catalysts for the Knoevenagel condensation reaction in the absence of a solvent. Particularly, 1-Zn featured high structural stability and enhanced the catalytic activity.

Catalytic C-H Bond Activation and Knoevenagel Condensation Using Pyridine-2,3-Dicarboxylate-Based Metal-Organic Frameworks

Three 1D coordination polymers (CPs) [M(pdca)(H2O)2] n (M = Zn, Cd, and Co; 1-3), and a 3D coordination framework {[(CH3)2NH2][CuK(2,3-pdca)(pa)(NO3)2]} n (4) (2,3-pdca = pyridine-2,3-dicarboxylate and pa = picolinic acid), have been synthesized adopting a solvothermal reaction strategy. The CPs have been thoroughly characterized using various spectral techniques, that is, elemental analyses, FT-IR, TGA, DSC, UV/vis, and luminescence. Structural information on 1-4 was obtained by PXRD and X-ray single-crystal analyses, whereas morphological insights were attained through FESEM, AFM, EDX, HRTEM, and BET surface area analyses. Roughness parameters were calculated from AFM analysis, whereas dimensions of small domains and interplanar spacing were defined with the aid of HRTEM. CPs 1-3 are 1D isostructural networks, whereas 4 is a 3D framework. Moreover, 1-4 display moderate luminescence at rt. In addition, 1-4 have been applied as economic and efficient porous catalysts for the Knoevenagel condensation reaction and C-H bond activation under mild conditions with good yields (95-98 and 97-99%), respectively. Notably, 1-3 can be reused up to seven cycles, whereas 4 can be reused up to five catalytic cycles with retained catalytic efficiency. Relative catalytic efficacy toward the Knoevenagel condensation reaction follows in the order 2 > 1 > 3 > 4, whereas 2 > 4 > 1 > 3 for C-H activation. The present result demonstrates synthetic, structural, optical, morphological, and catalytic aspects of 1-4.

A copper(ii)-based porous metal-organic framework for the efficient and rapid capture of toxic oxo-anion pollutants from water

The efficient and selective capture of toxic oxo-anions is highly desirable for environmental retrieval and hazardous waste disposal. This has remained an important task and gained considerable scientific attention due to their harmful effects on the ecosystem and human health. Herein, a porous cationic metal-organic framework (MOF), namely, [Cu₃Cl(L)(H₂O)₂]·Cl·4DMA·8H₂O (1), was synthesized (H₄L = 1,4,8,11-tetrazacyclotetradecane-N,N',N'',N'''-tetramethylenecinnamic acid and DMA = N,N'-dimethylacetamide). 1 shows high stability in aqueous solution and represents an extraordinary example that is capable of efficiently capturing environmentally toxic Cr₂O₇^2- and MnO₄^- anions. Moreover, the removal of Cr₂O₇^2- and MnO₄^- anions from water was also explored in the presence of other competing anions.

Functionalized resorcin[4]arene-based coordination polymers as heterogeneous catalysts for click reactions

One Cu(i) and two Cd(ii) coordination polymers have been achieved using a 4-mercaptopyridine-functionalized resorcin[4]arene. 1 exhibits predominant efficiency and excellent recyclability for the synthesis of 1,2,3-triazoles and β-OH-1,2,3-triazoles.

Halloysite nanotubes (HNTs)@ZIF-67 composites—a new type of heterogeneous catalyst for the Knoevenagel condensation reaction

Halloysite nanotubes (HNTs) are encapsulated in 50 nm thick shells of ZIF-67, producing novel nano-sized composites HNTs@ZIF-67.

Cavity-based applications of metallo-supramolecular coordination cages (MSCCs)

This review describes cavity-based applications of cage-like SCCs such as molecular recognition and separation, stabilization of reactive species by encapsulation, as drug delivery systems and as molecular flasks.

Calix[4]arene-based polyoxometalate organic–inorganic hybrid and coordination polymer as heterogeneous catalysts for azide–alkyne cycloaddition and Knoevenagel condensation reaction

One POM-based Cu(i)-hybrid and one Cd(ii) compound have been achieved by a calix[4]arene ligand. They exhibit efficient catalytic abilities for azide–alkyne cycloaddition and Knoevenagel condensation reactions, respectively.