Investigation into the Synthetic Strategies of Melamine-Based Porous Polymeric Materials: A Bibliometric Analysis

Recent years have seen the rapid development of melamine-based porous organic polymers, a new category of porous material. This review paper comprehensively describes the progress and trends of melamine-based porous organic polymers by using bibliometric analysis. A total of 1397 publications published over the previous 15 years were extracted from the Web of Science Core Collection database. Also, cooperation between countries and affiliations and keyword co-occurrence were assessed with the aid of VOS viewer software 1.6.20. The findings suggested that this field of study is now rapidly evolving. From 41 articles in 2009 to 180 articles in 2022, the number of published articles has increased significantly. China was the most productive nation, publishing 863 articles with 61.78% contribution. The Chinese Academy of Sciences was the most productive organization, and Chinese author Qiang Li was the most productive individual. Keyword co-occurrence analysis identified major research hotspots, including the design of high-surface-area materials for adsorption, functionalization strategies to enhance materials' performance, and novel synthesis routes for structural control. Furthermore, this review systematically categorizes synthetic strategies based on the linkage structures between melamine and other building blocks, providing insights into state-of-the-art advancements and future research directions in the field.

Supramolecular and molecular capsules, cages and containers

Stemming from early seminal notions of molecular recognition and encapsulation, three-dimensional, cavity-containing capsular compounds and assemblies have attracted intense interest due to the ability to modulate chemical and physical properties of species encapsulated within these confined spaces compared to bulk environments. With such a diverse range of covalent motifs and non-covalent (supramolecular) interactions available to assemble building blocks, an incredibly wide-range of capsular-type architectures have been developed. Furthermore, synthetic tunability of the internal environments gives chemists the opportunity to engineer systems for uses in sensing, sequestration, catalysis and transport of molecules, just to name a few. In this tutorial review, an overview is provided into the design principles, synthesis, characterisation, structural facets and properties of coordination cages, porous organic cages, supramolecular capsules, foldamers and mechanically interlocked molecules. Using seminal and recent examples, the advantages and limitations of each system are explored, highlighting their application in various tasks and functions.

Design and assembly of porous organic cages

Porous organic cages (POCs) represent a notable category of porous materials, showing remarkable material properties due to their inherent porosity. Unlike extended frameworks which are constructed by strong covalent or coordination bonds, POCs are composed of discrete molecular units held together by weak intermolecular forces. Their structure and chemical traits can be systematically tailored, making them suitable for a range of applications including gas storage and separation, molecular separation and recognition, catalysis, and proton and ion conduction. This review provides a comprehensive overview of POCs, covering their synthesis methods, structure and properties, computational approaches, and applications, serving as a primer for those who are new to the domain. A special emphasis is placed on the growing role of computational methods, highlighting how advanced data-driven techniques and automation are increasingly aiding the rapid exploration and understanding of POCs. We conclude by addressing the prevailing challenges and future prospects in the field.

Insights on the structural characteristics and molecular dynamic studies of methyl vanillin Schiff base bio-compounds

A new crystalline form of Schiff base, N-cyclohexyl-1-(3,4-dimethoxyphenyl)methanimine (CHADMB) was obtained from methanolic solution of cylohexylamine and (methylvanillin) 3,4dimethoxybenzaldehyde. Single crystal X-ray diffraction study reveals that the compound crystallized in monoclinic crystal system with P21/c space group having four molecules per unit cell (Z = 4). Hirshfeld surface (HS) analysis and 2D fingerprint plots reveals that weak non-covalent interactions are responsible for crystal packing. The UV-Vis spectroscopy study reveals that the optical band gap of the compound is 4.25 eV. The dielectric properties were studied as a function of frequency at room temperature and the results show that these properties can be exploited for optoelectronic applications. Thermal stability of the compound is revealed by thermogravimetric and differential thermogravimetric analysis. The in vitro antimicrobial activity against Gram negative (E. coli and P. aeruginosa and Gram positive (S. aureus ) bacterial strains and two fungal strains (C. albicans and A. niger) were studied by agar well diffusion method. It is found that the Schiff base is inhibiting the growth of the tested species to varying degrees. Molecular docking studies indicate that alkyl-pi and pi-pi weak interactions enhance the binding affinity of Schiff base-protein complexes. Molecular dynamics study reveals interaction of CHADMB complexed with bacterial protein, EC showed maximum stability which is in agreement with experimental result.Communicated by Ramaswamy H. Sarma.

Surface Engineering in Covalent Organic Polymers for High-Performance Li-S Batteries

Lithium-sulfur (Li-S) batteries are a promising energy storage technology due to their tempting high theoretical capacity and energy density. Nevertheless, the wastage of active materials that originates from the shuttling effect of polysulfides still hinders advancement of Li-S batteries. The effective design of cathode materials is extremely pivotal to solve this thorny problem. Herein, surface engineering in covalent organic polymers (COPs) has been performed to investigate the influence of pore wall polarity on the performance of COP-based cathodes used for Li-S batteries. With the assistance of experimental investigation and theoretical calculations, performance improvement by increasing pore surface polarity and a synergy effect of the polarized functionalities, along with nano-confinement effect of the COPs, are disclosed, to which the improved performance of Li-S batteries including outstanding Coulombic efficiency (99.0 %) and extremely low capacity decay (0.08 % over 425 cycles at 1.0 C) is attributed. This work not only enlightens the designable synthesis and applications of covalent polymers as polar sulfur hosts with high utilization of active materials, but also provides a feasible guide for the design of effective cathode materials for future advanced Li-S batteries.

Cross-linking reactions in Langmuir monolayers of specially designed aminolipids - a toolbox for the customized production of amphiphilic nanosheets

Synthetic amino lipids, already known as highly efficient gene therapy tool, are used in a novel way to create cross-linked stable one-molecule-thin films envisioned for future (bio)-materials applications. The films are prepared as Langmuir monolayers at the air/water interface and cross-linked 'in situ' via dynamic imine chemistry. The cross-linking process and the film characteristics are monitored by various surface-sensitive techniques such as grazing incidence X-ray diffraction, X-ray reflectivity, and infrared reflection-absorption spectroscopy. After transfer onto carbon grids, the cross-linked films are investigated by transmission and scanning electron microscopy. The obtained micrographs display mechanically self-supported nanosheets with area dimensions over several micrometers and, thus, an undeniable visual proof of successful cross-linking. The cross-linking process at the air/water interface allows to obtain Janus-faced sheets with a hydrophobic side characterized by aliphatic alkyl chains and a hydrophilic side characterized by nucleophilic groups like amines, hydroxyl groups and imine.

Polycage membranes for precise molecular separation and catalysis

The evolution of the chemical and pharmaceutical industry requires effective and less energy-intensive separation technologies. Engineering smart materials at a large scale with tunable properties for molecular separation is a challenging step to materialize this goal. Herein, we report thin film composite membranes prepared by the interfacial polymerization of porous organic cages (POCs) (RCC3 and tren cages). Ultrathin crosslinked polycage selective layers (thickness as low as 9.5 nm) are obtained with high permeance and strict molecular sieving for nanofiltration. A dual function is achieved by combining molecular separation and catalysis. This is demonstrated by impregnating the cages with highly catalytically active Pd nanoclusters ( ~ 0.7 nm). While the membrane promotes a precise molecular separation, its catalytic activity enables surface self-cleaning, by reacting with any potentially adsorbed dye and recovering the original performance. This strategy opens opportunities for the development of other smart membranes combining different functions and well-tailored abilities.

Evaluation of an Imine-Linked Polymer Organic Framework for Storage and Release of H2S and NO

Hydrogen sulfide (H₂S) and nitric oxide (NO) are especially known as toxic and polluting gases, yet they are also endogenously produced and play key roles in numerous biological processes. These two opposing aspects of the gases highlight the need for new types of materials to be developed in addition to the most common materials such as activated carbons and zeolites. Herein, a new imine-linked polymer organic framework was obtained using the inexpensive and easy-to-access reagents isophthalaldehyde and 2,4,6-triaminopyrimidine in good yield (64%) through the simple and catalyst-free Schiff-base reaction. The polymeric material has microporosity, an A_BET surface area of 51 m²/g, and temperature stability up to 300 °C. The obtained 2,4,6-triaminopyrimidine imine-linked polymer organic material has a higher capacity to adsorb NO (1.6 mmol/g) than H₂S (0.97 mmol/g). Release studies in aqueous solution showed that H₂S has a faster release (3 h) from the material than NO, for which a steady release was observed for at least 5 h. This result is the first evaluation of the possibility of an imine-linked polymer organic framework being used in the therapeutic release of NO or H₂S.

Purely Covalent Molecular Cages and Containers for Guest Encapsulation

Cage compounds offer unique binding pockets similar to enzyme-binding sites, which can be customized in terms of size, shape, and functional groups to point toward the cavity and many other parameters. Different synthetic strategies have been developed to create a toolkit of methods that allow preparing tailor-made organic cages for a number of distinct applications, such as gas separation, molecular recognition, molecular encapsulation, hosts for catalysis, etc. These examples show the versatility and high selectivity that can be achieved using cages, which is impossible by employing other molecular systems. This review explores the progress made in the field of fully organic molecular cages and containers by focusing on the properties of the cavity and their application to encapsulate guests.

Transformation of Porous Organic Cages and Covalent Organic Frameworks with Efficient Iodine Vapor Capture Performance

The reaction of 5,5'-([2,2'-bipyridine]-5,5'-diyl)diisophthalaldehyde (BPDDP) with cyclohexanediamine and [benzidine (BZ)/[2,2'-bipyridine]-5,5'-diamine (BPDA)], respectively, affords a nitrogen-rich porous organic cage BPPOC and two two-dimensional (2D) covalent organic frameworks (COFs), USTB-1 and USTB-2 (USTB = University of Science and Technology Beijing), under suitable conditions. Interestingly, BPPOC with a single-crystal X-ray diffraction structure is able to successfully transform into USTB-1 and USTB-2 (newly converted COFs denoted as USTB-1c and USTB-2c, respectively) upon exchange of the imine unit of cyclohexanediamine in the cage by BZ and BPDA. Such a transformation also enables the isolation of analogous COFs (USTB-3c and USTB-4c) on the basis of an isostructural organic cage, BTPOC, which is derived from 5,5'-([2,2'-bithiophene]-4,4'-diyl)diisophthalaldehyde (BTDDP) and cyclohexanediamine. However, the conventional solvothermal reaction between BTDDP and BPDA leads to an impure phase of USTB-4 containing incompletely converted aldehyde groups due to the limited solubility of the building block. The newly prepared COFs have been characterized by nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. In particular, BPPOC is able to absorb the iodine vapor with an uptake of 5.64 g g^-1, breaking the porous organic cage's (POC's) record value of 3.78 g g^-1. Nevertheless, the cage-derived COFs exhibit improved iodine vapor adsorption capability in comparison with the directly synthesized counterparts, with the highest uptake of 5.80 g g^-1 for USTB-1c. The mechanism investigation unveils the superiority of nitrogen atoms to sulfur atoms for POCs in iodine vapor capture with the assistance of definite crystal structures. This, in combination with porosity, synergistically influences the iodine vapor capture capacity of COFs.

Controlling chirality in the synthesis of 4 + 4 diastereomeric amine macrocycles derived from trans-1,2-diaminocyclopentane and 2,6-diformylpyridine

A few suitably long dialdehyde and primary diamine building blocks of a predetermined chirality have been designed and synthesized to enable controlled and efficient synthesis of all six possible diastereomers of 4 + 4 macrocyclic amine derived from trans-1,2-diaminocyclopentane (DACP) and 2,6-diformypyridine (DFP) units. Although two out of six diastereomers have been reported recently, their synthesis presented here is more direct and occurs with an improved yield. This family of 4 + 4 macrocycles contains one pair of homochiral enantiomers of identical RRRRRRRR and SSSSSSSS configurations of DACP units, two different meso forms (meso I of alternating RRSSRRSS and meso II of neighboring RRRRSSSS configuration of DACP moieties) as well as one pair of heterochiral enantiomers, where configuration of one diamine fragment is opposite to the other three diamine parts, RRRRRRSS and SSSSSSRR, respectively. The structures of each type of macrocycle in solid state have been confirmed by single crystal analyses of a macrocyclic amine in its suitable protonated form. The different symmetry of each type of macrocycle in solutions has been proved by ¹H and ¹³C NMR spectra of their hydrochloride derivatives. The chiral nature of two different pairs of optically active enantiomers has been established by circular dichroism spectra. These chiral 4 + 4 diastereomeric macrocycles are receptors for chiral guests and recognize in solution 10-camphorsulfonic acid as well as chiral tartaric acid.

High-performance electrocatalyst based on polyazine derived mesoporous nitrogen-doped carbon for oxygen reduction reaction

Nitrogen-doped porous carbon materials have high potential in metal-free electrocatalysts, which is essential for several renewable energy conversion systems. Herein, we report a convenient and environment-friendly method to fabricate a nitrogen doped mesoporous carbon (NMC) using a nonionic surfactant of Pluronic F127 micelles as the template and a Schiff-base polymer (polyazine) as the precursor. The synthesized NMCs were of spheric morphology and mesoporous structures with surface area up to 1174 m² g⁻¹ and high level of nitrogen (2.9–19 at%) and oxygen (4.9–7.4 at%) simultaneously doped. The electrochemical data of NMCs were analyzed in the context of the BET and XPS information. A correlation between ORR activity and the pyridinic-N was found. The NMC-700 demonstrate the highest electrocatalytic activity for ORR among the studied materials, which can be ascribed to the reasonable surface area and mesoporous structure, as well as the most abundant touchable pyridinic-N, thus providing more effective active sites for the oxygen reduction. In comparsion to the control sample, the NMC-700 provides the ORR electrocatalytic activity approximate to that of commercial Pt/C catalyst with a highly long-term stability.

Nitrogen-doped porous carbon materials have high potential in metal-free electrocatalysts, which is essential for several renewable energy conversion systems.

Synthesis of hypercrosslinked polymers for efficient solid-phase microextraction of polycyclic aromatic hydrocarbons and their derivatives followed by gas chromatography-mass spectrometry determination

Three novel hypercrosslinked polymers (HCPs) were synthesized via Friedel-Crafts reaction employing 1,3,5-tris(bromomethyl)-2,4,6-trimethylbenzene as alkylating agent, and triphenylbenzene, tetraphenylethylene and p-quaterphenyl as the aromatic units, respectively. The prepared HCPs were applied as solid-phase microextraction coatings for direct immersion extraction of polycyclic aromatic hydrocarbons (PAHs) and their oxygenated and nitrated derivatives in environmental water samples. The key factors affecting the extraction efficiency including extraction time, extraction temperature, stirring rate, ionic strength and desorption conditions, were carefully studied. Coupled with gas chromatography mass spectrometry analysis, a new method for determining PAHs and their derivatives was developed. Under the optimized conditions, the limits of detection (S/N=3) and limits of quantitation (the lowest concentration for quantification) of the method were in the range of 2.5-25.0 and 7.5-75.0 ng L^-1, respectively. The recoveries of spiked samples were in the range of 73.1-118.3% with relative standard deviations less than 13.0%. The developed method was applied for the simultaneous determination of nine PAHs and their derivatives in environmental water samples, showing good accuracy and reliability.

An azine-based polymer derived hierarchically porous N-doped carbon for hydrophilic dyes removal

In this study, a novel hierarchically porous N-doped carbon (HPNC) material was successfully prepared by soft-templating method. The commercial triblock copolymer of Pluronic F127 and a polyazine derived from hydrazine hydrate & glyoxal were used as soft template and precursor, respectively. The obtained materials were fully characterized and tested as a sorbent for the removal of hydrophilic dyes of Methylene blue (MB), Basic Fuchsin (BF), Eosin Y (EY) and Rhodamine B (RB) from their aqueous effluents. According to the characterization results, the synthesized material of HPNC-1000 presented thick fibrous morphology with micron size in diameter, hierarchically porous structure with surface area of 1853 m²/g, pore volume of 1.59 cm³/g and nitrogen content of 4.5 wt%. Adsorption-desorption investigation reveals that synergistic effect of hydrophobic interaction and hydrogen-bonding formation of the dye molecules with the sorbent was most pronounced in the adsorptions. The maximum adsorption capacities for MB, BF, EY and RB reached 0.83, 0.92, 1.23 and 1.83 mmol g^-1, respectively. The adsorption processes well fitted by the pseudo first-order kinetic model and the Liu's isotherm. The sorbent can be regenerated by above 90% of the initial adsorption efficiency after six regeneration cycles.

Crystalline Porous Materials for Nonlinear Optics

Crystalline porous materials have been extensively explored for wide applications in many fields including nonlinear optics (NLO) for frequency doubling, two-photon absorption/emission, optical limiting effect, photoelectric conversion, and biological imaging. The structural diversity and flexibility of the crystalline porous materials such as the metal-organic frameworks, covalent organic frameworks, and polyoxometalates provide numerous opportunities to orderly organize the dipolar chromophores and to systemically modify the type and concentration of these dipolar chromophores in the confined spaces, which are highly desirable for NLO. Here, the recent advances in the crystalline porous NLO materials are discussed. The second-order NLO of crystalline porous materials have been mainly devoted to the chiral and achiral structures, while the third-order NLO crystalline porous materials have been categorized into pure organic and hybrid organic/inorganic materials. Some representative properties and applications of these crystalline porous materials in the NLO regime are highlighted. The future perspective of challenges as well as the potential research directions of crystalline porous materials have been also proposed.

Organic cage supported metal nanoparticles for applications

Porous shape-persistent organic cages can anchor metal nanoparticles either inside the cavity or in the external cavity generated through self-assembly. The size of these nanoparticles range from 1-2 nm depending upon the host and can be controlled within a narrow size distribution. The nanoparticles thus formed are quite stable as they are segregated efficiently preventing their association and eventual precipitation. These fine nanoparticles are found to be quite effective in catalyzing a number of organic transformations besides showing interesting emission properties.

Solvent-controlled self-assembly of tetrapodal [4 + 4] phosphate organic molecular cage

Two flexible subcomponents, namely tris(4-formylphenyl)phosphate and tris(2-aminoethyl)amine, are assembled into a tetrapodal [4 + 4] cage depending on the solvent effect. Single-crystal structure analysis reveals that the caivity is surrounded by four phosphate uints. Good selectivity of CO₂ adsorption over CH₄ is demonstrated by the gas adsorption experiment.

A convenient one-pot nanosynthesis of a C(sp2)-C(sp3)-linked 3D grid via an 'A2 + B3' approach

Fluorene-based 3D-grid-FTPA was synthesised with a total yield of 55% via the one-pot formation of six C(sp²)-C(sp³) bonds through a BF₃·Et₂O-mediated Friedel-Crafts reaction of A₂-type bifluorene tertiary alcohol (BIOH) and two B₃-type triphenylamines. At the same time, Un-grid-FTPA (2.7%) and 2D-grid-FTPA (5.6%) were obtained as by-products from this synthesis method. In addition, the effect of stereoisomers of BIOH was evaluated to demonstrate that Rac-BIOH is a better A₂-type building block to prepare 3D-grid-FTPA in a relatively high yield. Furthermore, 3D-grid-FTPA showed excellent chemical, thermal, and photo-stabilities.

A Robust Nonvolatile Resistive Memory Device Based on a Freestanding Ultrathin 2D Imine Polymer Film

Here, the synthesis of a wafer-scale ultrathin 2D imine polymer (2DP) film with controllable thickness from simple benzene-1,3,5-tricarbaldehyde (BTA) and p-phenylenediamine (PDA) building blocks is reported using a Schiff base polycondensation reaction at the air-water interface. The synthesized freestanding 2DP films are porous, insulating, and more importantly, covalently linked, which is ideally suited for nonvolatile memristors that use a conductive filament mechanism. These devices exhibit excellent switching performance with high reliability and reproducibility, with on/off ratios in the range of 10² to 10⁵ depending on the thickness of the film. In addition, the endurance and data retention capability of 2DP-based nonvolatile resistive memristors are up to 200 cycles and 8 × 10⁴ s under constant voltage stress at 0.1 V. The intrinsic flexibility of the covalent organic polymer enables the fabrication of a flexible memory device on a polyimide film, which exhibits as reliable memory performance as that on the rigid substrate. Moreover, the 2DP-based memory device shows outstanding thermal stability and organic solvent resistance, which are desirable properties for applications in wearable devices.

Organic Imine Cages: Molecular Marriage and Applications

Imine condensation has been known to chemists for more than a century and is used extensively to synthesize large organic cages of defined shapes and sizes. Surprisingly, in the context of the synthetic methods for organic imine cages (OICs), a self-sorting/self-selection (molecular marriage) process has been overlooked over the years. Such processes are omnipresent in nature, from the creation of galaxies to the formation of the smallest building blocks of life (the cell). Such processes have the incredible ability to guide a system toward the formation of a specific product or products out of a collection of equally probable multiple possibilities. This Minireview sheds light on new opportunities in cage design offered by the self-sorting/self-selection protocol in OICs. Recent efforts to explore organic cages for various exciting new applications are discussed; for example, for detection of harmful small organic molecules, as templates for nucleation of metal nanoparticles (MNPs), and as proton-conducting materials.

Hyper-Cross-linked Porous Organic Frameworks with Ultramicropores for Selective Xenon Capture

Exceptionally stable ultramicroporous C-C-bonded porous organic frameworks (IISERP-POF6, 7, 8) have been prepared using simple Friedel-Crafts reaction. These polymers exhibit permanent porosity with a Brunauer-Emmett-Teller surface area of 645-800 m²/g. Xe/Kr adsorptive separation has been carried out with these polymers, and they display selective Xe capture ( s(Xe/Kr) = 6.7, 6.3, and 6.3) at 298 K and 1 bar pressure. Interestingly, these polymers also show remarkable Xe/N₂ ( s(Xe/N₂) = 200, 180, and 160 at 298 K and 1 bar) and Xe/CO₂ selectivity ( s(Xe/CO₂) = 5.6, 7.4, and 5.6) for a 1:99 composition of Xe-N₂/Xe-CO₂. Selective removal of Xe at such low concentrations is extremely challenging; the observed selectivities are higher compared to those observed in porous carbons and metal-organic frameworks. Breakthrough studies were performed using the composition relevant to the nuclear off-gas mixture with the polymers, and we find that the polymers hold Xe for a longer time in the column, which illustrates the Xe/Kr separation performance under dynamic conditions.

Functional π-Conjugated Two-Dimensional Covalent Organic Frameworks

Fingerprints of π-conjugated compounds are ubiquitous in nature and play a crucial part in human existence. For instance, cis-retinal, an endogenous π-conjugated molecule present in the eye, performs a vital role in the function of visual perception. π-Conjugated molecules have also received a great deal of attention owing to their intriguing optical properties and created a surge in optoelectronics. Varieties of π-conjugated molecules/oligomers have been developed and explored for a number of applications such as organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), organic photovoltaics (OPVs), and sensors, among others. While the extended π-delocalization in one-dimensional (1D) polymers versus oligomers produce superior optical and electronic properties, further extension of π-delocalization to the second dimension (2D) is expected to give rise even more intriguing properties as revealed by theoretical studies. As a matter of fact, graphene is the best example of 2D-conjugated polymers, but its zero-band-gap behavior is a major impediment for semiconducting applications. In contrast, it was challenging to prepare 2D crystalline polymers until the discovery of boroxine/boronate ester linked covalent organic frameworks (COFs) by Yaghi and co-workers. COFs are a new class of porous crystalline polymers in which organic building blocks are held together by covalent bonds. These polymers exhibit potential applications in gas storage, energy storage, photocatalyst, heterogeneous catalysis, sensors, etc. However, the first π-conjugated COF was realized in 2009 via the introduction of imine linker (-C═N-) between the building blocks. Since then, wide varieties of COFs with various π-delocalization promoting spacers have been developed and explored their electronic and optical properties and pertinent applications. In this review, we will highlight the importance of 2D π-conjugated COFs and their achievements in developing novel functionalities.

Cage Based Crystalline Covalent Organic Frameworks

The first two cage based crystalline covalent organic frameworks, cage-COF-1 and cage-COF-2, were constructed from a prism-like three-aldehyde-containing molecular cage. The cage contains two horizontal phloroglucinol and three vertical triazine moieties forming three identical V-shaped cavities. By reacting with p-phenylenediamine and 4,4'-biphenyldiamine, the two cage-COFs were formed with a hexagonal skeleton and possess a unique structure. Due to the pillared cage nodes, the linkers are hanging with their π-surfaces but not C-H sites exposed to the pore, and enjoy certain rotational dynamics as suggested by ¹³C CP/MAS NMR. The antidirection of the diimine linkages leads to rippled layers which pack in unique ABC mode through alternate stacking of the cage twosided faces in both AB and AC layers. Such packing forms trigonal channels along c axis which are interconnected in ab plane due to the large open space created across the hanging linkers, resembling the porous characteristics of 3D COFs. The cage-COFs have a permanent porosity and can adsorb CO₂ facilitated by the intrinsic cage cavities that serve as prime adsorption sites. The unprecedented cage-COFs not only merge the borderline of 2D and 3D COFs but also bridge porous organic cages to extended crystalline organic frameworks.

Crystal structure of N-phenyl-2-(propan-2-ylidene)hydrazine-1-carbothioamide, C10H13N3S

C10H13N3S, monoclinic, P21/c (no. 14), a = 12.2463(8) Å, b = 7.6397(5) Å, c = 11.6544(9) Å, β = 102.684(2)°, V = 1060.72(11) Å3, Z = 4, Rgt(F) = 0.0448, wRref(F2) = 0.1211, T = 301(2) K.

Adaptive responses of sterically confined intramolecular chalcogen bonds

The existence of intramolecular chalcogen bonds (IChBs) in 2,6-disubstituted arylchalcogen derivatives is determined by the substituents and the sigma hole donor behavior of the chalcogen atom in the molecule.

The responsive behavior of an entity towards its immediate surrounding is referred to as an adaptive response. The adaptive responses of a noncovalent interaction at the molecular scale are reflected from its structural and functional roles. Intramolecular chalcogen bonding (IChB), an attractive interaction between a heavy chalcogen E (E = Se or Te) centered sigma hole and an ortho-heteroatom Lewis base donor D (D = O or N), plays an adaptive role in defining the structure and reactivity of arylchalcogen compounds. In this perspective, we describe the adaptive roles of a chalcogen centered Lewis acid sigma hole and a proximal Lewis base (O or N) in accommodating built-in steric stress in 2,6-disubstituted arylchalcogen compounds. From our perspective, the IChB components (a sigma hole and the proximal Lewis base) act in synergism to accommodate the overwhelming steric force. The adaptive responses of the IChB components are inferred from the observed molecular structures and reactivity. These include (a) adaptation of a conformation without IChBs, (b) adaptation of a conformation with weak IChBs, (c) twisting the skeletal aryl ring while maintaining IChBs, (d) ionization of the E–X bond (e.g., X = Br) to relieve stress and (e) intramolecular cyclization to relieve steric stress. A comprehensive approach, involving X-ray data analysis, density functional theory (DFT) calculations, reaction pattern analysis and principal component analysis (PCA), has been employed to rationalize the adaptive behaviors of IChBs in arylchalcogen compounds. We believe that the perception of ChB as an adaptive/stimulus responsive interaction would profit the futuristic approaches that would utilise ChB as self-assembly and molecular recognition tools.

Synthesis of Sub-10 nm Two-Dimensional Covalent Organic Thin Film with Sharp Molecular Sieving Nanofiltration

We demonstrated here a novel and facile synthesis of two-dimensional (2D) covalent organic thin film with pore size around 1.5 nm using a planar, amphiphilic and substituted heptacyclic truxene based triamine and a simple dialdehyde as building blocks by dynamic imine bond formation at the air/water interface using Langmuir-Blodgett (LB) method. Optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM), all unanimously showed the formation of large, molecularly thin and free-standing membrane that can be easily transferred on different substrate surfaces. The 2D membrane supported on a porous polysulfone showed a rejection rate of 64 and 71% for NaCl and MgSO₄, respectively, and a clear molecular sieving at molecular size around 1.3 nm, which demonstrated a great potential in the application of pretreatment of seawater desalination and separation of organic molecules.

A Facile Approach to Prepare Multiple Heteroatom-Doped Carbon Materials from Imine-Linked Porous Organic Polymers

In this paper, we proposed a new strategy to prepare multiple heteroatom doped (N, P-doped) porous carbon materials with high surface area of ~1,535 m² g⁻¹ simply by pyrolysis of imine-linked porous organic polymers (POPs) synthesized via Schiff base condensation. The strategy is simple without any post-processing and various heteroatoms could be involved. Scanning electron microscopy, Raman spectra, Nitrogen gas adsorption-desorption, X-ray photoelectron spectroscopy have been used to characterize the morphology, the structure and the composition of the materials. The multiple heteroatom doped porous carbon materials also display high electrocatalytic performance as exampled by the application in oxygen reduction, which showed the catalyst favors 4-electron transfer during the process, along with superior stability and higher tolerance to methanol as compared to the Pt/C. These results indicate the present method is promising for the preparation of multi-heteroatom doped carbon materials in the application of electrocatalysis.

Two metal–organic frameworks based on pyridyl–tricarboxylate ligands as size-selective catalysts for solvent-free cyanosilylation reaction

Two novel 3D metal–organic frameworks based on multifunctional pyridyl–tricarboxylate ligands as size-selective heterogeneous catalysts for the cyanosilylation of acetaldehydes.

Porous organic cage stabilised palladium nanoparticles: efficient heterogeneous catalysts for carbonylation reaction of aryl halides

Porous organic cage stabilised palladium nanoparticles were prepared using methanol as a mild reductant and displayed high catalytic activity for the carbonylation reaction of aryl halides under mild conditions.