High-Entropy Lanthanide-Organic Framework as an Efficient Heterogeneous Catalyst for Cycloaddition of CO2 with Epoxides and Knoevenagel Condensation.

Multimetallic synergistic effects have the potential to improve CO2 cycloesterification and Knoevenagel reaction processes, outperforming monometallic MOFs. The results demonstrate superior performance in these processes. To investigate this, we created and characterized a selection of single-component Ln(III)-MOFs (Ln = Eu, Tb, Gd, Dy, Ho) and high-entropy lanthanide-organic framework (HE-LnMOF) using solvent-thermal conditions. The experiments revealed that HE-LnMOF exhibited heightened catalytic efficiency in CO2 cycloesterification and Knoevenagel reactions compared to single-component Ln(III) MOFs. Moreover, the HE-LnMOF displayed significant stability, maintaining their structural integrity after five cycles while sustaining elevated conversion and selectivity rates. The feasible mechanisms of catalytic reactions were also discussed. HE-LnMOF possess multiple unsaturated metal centers, acting as Lewis acid sites, with oxygen atoms connecting the metal, and hydroxyl groups on the ligand serving as base sites. This study introduces a novel method for synthesizing HE-LnMOF and presents a fresh application of HE-LnMOF for converting CO2.

Completely Inorganic Deep Eutectic Solvents for Efficient and Recyclable Liquid-Liquid Interface Catalysis.

Organic acid-based deep eutectic solvents (DESs) as catalysts always suffer from weak stability and low recyclability due to the accumulation of organic oxidative products in the DES phase. Herein, a completely inorganic deep eutectic solvent (IDES) ZnCl2/PA with zinc chloride (ZnCl2) and phosphoric acid (PA) as precursors is constructed to realize liquid-liquid interface catalysis for desulfurization of fuel and product self-separation for the first time. Owing to the inorganic nature, the organic oxidative products are accumulated at the interface between the IDES and fuel rather than the IDES phase. With this unique feature, the IDES can be reused for at least 15 times without any further treatment in oxidative desulfurization process, showing a state-of-the-art cycle-regeneration stability. Moreover, compared with the reported organic DESs, the IDES also reveals more attractive catalytic oxidative desulfurization performance. Experimental and theoretical studies indicate that the strong coordination Zn···O═P and the strong adsorption energy between IDES and sulfides enhance the activation of H2O2 to reactive oxygen species, leading to the superior catalytic performance in oxidative desulfurization of fuel.

Rational Design of Porous Ionic Liquids for Coupling Natural Gas Purification with Waste Gas Conversion.

Removal of trace impurities for natural gas purification coupled with waste gas conversion is highly desired in industry. We here report a type of porous ionic liquids (PILs) that can realize the continuous flow separation of CH4 /CO2 /H2 S and the conversion of the captured H2 S to useful products. The PILs are synthesized through a step-by-step surface modification of ionic liquids (ILs) onto UiO-66-OH nanocrystals. The introduction of free tertiary amine groups on the nanocrystal surface endows these PILs with an exceptional ability to enrich H2 S from CO2 and CH4 with impressive selectivity, while the permanent pores of UiO-66-OH act as containers to store an exceptionally higher amount of the selectively captured H2 S than the corresponding nonporous ILs. Simultaneously, the tertiary amines as dual functional moieties offer effective catalytic sites for the conversion of the H2 S stored in PILs into 3-mercaptoisobutyric acid, a key intermediate required for the synthesis of Captopril (an antihypertensive drug). Molecular dynamics, density functional theory calculations and Grand Canonical Monte Carlo simulations help understand both the mechanisms of separation and catalysis performance, confirming that the tertiary amines as well as the permanent pores in UiO-66-OH play vital roles in the whole procedure.

Reimplementing Guest Shape Sorting of Nonporous Adaptive Crystals via Substituent-Size-Dependent Solid-Vapor Postsynthetic Modification.

Postsynthetic modification (PSM) has been widely used in porous crystalline materials to gain better performance in adsorptive separation of gases or hydrocarbons. We here report that guest adsorption selectivity in a kind of nonporous crystalline materials, namely nonporous adaptive crystals (NACs), can be readily and precisely tuned via a facile substituent-size-dependent solid-vapor PSM method. Before PSM, NACs of pillar[4]arene[1]quinone EtP4Q1 show negligible selectivity for C5 hydrocarbons. PSM with a larger substituent, cyclopentylamine, onto EtP4Q1 NACs does not improve the selectivity, while EtP4Q1 NACs after PSM with a slightly smaller substituent, cyclobutylamine, is endowed with very high preference of n-pentane over cyclopentane. Comprehensive structural analyses confirm that the intermolecular interactions among the host compounds and host-guest interactions between the adsorbent and the adsorbate are the two major factors in determining the guest selectivity.

Separation of pyrrolidine from tetrahydrofuran by using pillar[6]arene-based nonporous adaptive crystals.

Pyrrolidine, an important feedstock in the chemical industry, is commonly produced via vapor-phase catalytic ammoniation of tetrahydrofuran (THF). Obtaining pyrrolidine with high purity and low energy cost has extremely high economic and environmental values. Here we offer a rapid and energy-saving method for adsorptive separation of pyrrolidine and THF by using nonporous adaptive crystals of per-ethyl pillar[6]arene (EtP6). EtP6 crystals show a superior preference towards pyrrolidine in 50 : 50 (v/v) pyrrolidine/THF mixture vapor, resulting in rapid separation. The purity of pyrrolidine reaches 95% in 15 min of separation, and after 2 h, the purity is found to be 99.9%. Single-crystal structures demonstrate that the selectivity is based on the stability difference of host-guest structures after uptake of THF or pyrrolidine and non-covalent interactions in the crystals. Besides, EtP6 crystals can be recycled efficiently after the separation process owing to reversible transformations between the guest-free and guest-loaded EtP6.

Engineering Permanent Porosity into Liquids.

The possibility of engineering well-defined pores into liquid materials is fascinating from both a conceptual and an applications point of view. Although the concept of porous liquids was proposed in 2007, these materials had remained hypothetical due to the technical challenges associated with their synthesis. Over the past five years, however, reports of the successful construction of porous liquids based on existing porous scaffolds, such as coordination cages, organic cages, metal-organic frameworks, porous carbons, zeolites, and porous polymers, have started to emerge. Here, the focus is on these early reports of porous liquids as prototypes in the field, classified according to the previously defined types of porous liquids. Particular attention will be paid to design strategies and structure-property relationships. Porous liquids have already exhibited promising applications in gas storage, transportation, and chemical separations. Thus, they show great potential for use in the chemical industry. The challenges of preparation, scale-up, volatility, thermal and chemical stability, and competition with porous solids will also be discussed.

Selective Separation of Methylfuran and Dimethylfuran by Nonporous Adaptive Crystals of Pillararenes.

The separation of 2-methylfuran (MeF) and 2,5-dimethylfuran (DMeF) mixtures is very important in the chemical industry. Herein, we offer a novel strategy for the separation of MeF and DMeF using nonporous adaptive crystals (NACs) of perethylated pillar[5]arene (EtP5), perethylated pillar[6]arene (EtP6), perbromoethylated pillar[5]arene (BrP5), and perbromoethylated pillar[6]arene (BrP6). We find that the crystals of EtP6 and BrP5 show remarkable selectivities for MeF in a 50:50 (v/v) MeF:DMeF mixture vapor, yielding purities of 94.0 and 96.3%, respectively. Single-crystal structures reveal that these different selectivities come from the different thermodynamic stabilities and binding modes of the host-guest complexes. Cycling experiments demonstrate that these crystals can be reused more than five cycles without loss of performance.

Transformation of Nonporous Adaptive Pillar[4]arene[1]quinone Crystals into Fluorescent Crystals via Multi-Step Solid-Vapor Postsynthetic Modification for Fluorescence Turn-on Sensing of Ethylenediamine.

Organic solid-state fluorescent crystals have received extensive attention owing to their remarkable and promising optoelectronic applications in many fields. Current methods to obtain organic fluorescent crystals usually involve two steps: (1) solution phase organic synthesis and (2) crystallization of target fluorescent compounds. Direct transformation from nonfluorescent organic crystals to fluorescent organic crystals by postsynthetic modification (PSM) might be a potential alternative to the traditional methods. Although it is common to implement PSM for porous frameworks, it remains a huge challenge for nonporous organic crystals. Herein, we report a novel method of multistep solid-vapor PSM in nonporous adaptive crystals (NACs) of a pillar[4]arene[1]quinone (M1) to prepare organic solid-state fluorescent crystals. Fluorescent organic crystals can be simply generated when guest-free M1 crystals were exposed to ethylenediamine (EDA) vapor. However, only nonemissive crystals of a thermodynamically metastable intermediate M2 are obtained through solid-vapor single-crystal-to-single-crystal transformation of CH3CN-loaded M1 crystals. Solution-phase reaction of M1 with EDA affords three distinct compounds with different fluorescent properties, which are demonstrated to be the main components of the fluorescent organic crystals that are generated by the solid-vapor PSM. Mechanistic studies show that the pillararene skeleton not only induces the solid-vapor PSM by physical adsorption of EDA but also facilitates the fluorescent emission in the solid state by restricting intermolecular π-π interactions to avoid aggregation-caused quenching (ACQ). Furthermore, this interesting phenomenon is applied for facile fluorescence turn-on sensing of EDA vapor to distinguish EDA from other aliphatic amines.

Facile benzene reduction promoted by a synergistically coupled Cu-Co-Ce ternary mixed oxide.

Hydrogenation of aromatic rings promoted by earth-abundant metal composites under mild conditions is an attractive and challenging subject in the long term. In this work, a simple active site creation and stabilization strategy was employed to obtain a Cu+-containing ternary mixed oxide catalyst. Simply by pre-treatment of the ternary metal oxide precursor under a H2 atmosphere, a Cu+-derived heterogeneous catalyst was obtained and denoted as Cu1Co5Ce5O x . The catalyst showed (1) high Cu+ species content, (2) a uniform distribution of Cu+ doped into the lattices of CoO x and CeO2, (3) formation of CoO x /CuO x and CeO2/CuO x interfaces, and (4) a mesoporous structure. These unique properties of Cu1Co5Ce5O x endow it with pretty high hydrogenation activity for aromatic rings under mild conditions (100 °C with 5 bar H2), which is much higher than that of the corresponding binary counterparts and even exceeds the performance of commercial noble metal catalysts (e.g. Pd/C). The synergetic effect plays a crucial role in the catalytic procedure with CeO2 functioning as a hydrogen dissociation and transfer medium, Cu+ hydrogenating the benzene ring and CoO x stabilizing the unstable Cu+ species. This will unlock a new opportunity to design highly efficient earth-abundant metal-derived heterogeneous catalysts via interface interactions.

Highly Selective Removal of Trace Isomers by Nonporous Adaptive Pillararene Crystals for Chlorobutane Purification.

Removal of trace chlorobutane (CB) isomers is highly desired to produce high grade 1-chlorobutane (1-CB) and 2-chlorobutane (2-CB). Here, we report that nonporous adaptive crystals (NACs) of perethylated pillar[5]arene (EtP5) and pillar[6]arene (EtP6) effectively remove trace CB isomers. EtP5 NACs can remove trace 1-CB (2%) from 2-CB to improve its purity from 98.0% to 99.9%, while EtP6 NACs can remove trace 2-CB from 1-CB to improve its purity from 98.0% to 99.9%. The adsorption of trace CB isomers results in the formation of new CB-loaded crystal structures, whose thermostability is higher than their corresponding isomer-loaded structures. This determines the selectivity of NACs toward the trace CB isomers. Reversible transformations between nonporous guest-free and guest-loaded structures make EtP5 and EtP6 highly recyclable.

Vapochromic crystals: understanding vapochromism from the perspective of crystal engineering.

Vapochromic materials, which undergo colour and/or emission changes upon exposure to certain vapours or gases, have received increasing attention recently because of their wide range of applications in, e.g., chemical sensors, light-emitting diodes, and environmental monitors. Vapochromic crystals, as a specific kind of vapochromic materials, can be investigated from the perspective of crystal engineering to understand the mechanism of vapochromism. Moreover, understanding the vapochromism mechanism will be beneficial to design and prepare task-specific vapochromic crystals as one kind of low-cost 'electronic nose' to detect toxic gases or volatile organic compounds. This review provides important information in a broad scientific context to develop new vapochromic materials, which covers organometallic or coordination complexes and organic crystals, as well as the different mechanisms of the related vapochromic behaviour. In addition, recent examples of supramolecular vapochromic crystals and metal-organic-framework (MOFs) vapochromic crystals are introduced.

Mechanochemical synthesis of pillar[5]quinone derived multi-microporous organic polymers for radioactive organic iodide capture and storage.

The incorporation of supramolecular macrocycles into porous organic polymers may endow the material with enhanced uptake of specific guests through host-guest interactions. Here we report a solvent and catalyst-free mechanochemical synthesis of pillar[5]quinone (P5Q) derived multi-microporous organic polymers with hydrophenazine linkages (MHP-P5Q), which show a unique 3-step N2 adsorption isotherm. In comparison with analogous microporous hydrophenazine-linked organic polymers (MHPs) obtained using simple twofold benzoquinones, MHP-P5Q is demonstrated to have a superior performance in radioactive iodomethane (CH3I) capture and storage. Mechanistic studies show that the rigid pillar[5]arene cavity has additional binding sites though host-guest interactions as well as the halogen bond (-I⋯N = C-) and chemical adsorption in the multi-microporous MHP-P5Q mainly account for the rapid and high-capacity adsorption and long-term storage of CH3I.

Highly Selective Separation of Minimum-Boiling Azeotrope Toluene/Pyridine by Nonporous Adaptive Crystals of Cucurbit[6]uril.

The production of high purity toluene and pyridine is of significance in both industrial production and synthetic chemistry. The present protocols available to separate toluene/pyridine mixtures are several energy-intensive distillation methods, which are not environmentally friendly and cost-effective. Herein, we provide an energy-efficient and simple adsorptive separation protocol using nonporous adaptive crystals of cucurbit[6]uril (Q[6]). Q[6] crystals separate pyridine from toluene/pyridine mixtures with nearly 100 % purity. Furthermore, removal of the guest from guest-loaded Q[6] leads to the guest-free cucurbit[6]uril, which can be recycled without losing performance.

Supramolecular-Macrocycle-Based Crystalline Organic Materials.

Supramolecular macrocycles are well known as guest receptors in supramolecular chemistry, especially host-guest chemistry. In addition to their wide applications in host-guest chemistry and related areas, macrocycles have also been employed to construct crystalline organic materials (COMs) owing to their particular structures that combine both rigidity and adaptivity. There are two main types of supramolecular-macrocycle-based COMs: those constructed from macrocycles themselves and those prepared from macrocycles with other organic linkers. This review summarizes recent developments in supramolecular-macrocycle-based COMs, which are categorized by various types of macrocycles, including cyclodextrins, calixarenes, resorcinarenes, pyrogalloarenes, cucurbiturils, pillararenes, and others. Effort is made to focus on the structures of supramolecular-macrocycle-based COMs and their structure-function relationships. In addition, the application of supramolecular-macrocycle-based COMs in gas storage or separation, molecular separation, solid-state electrolytes, proton conduction, iodine capture, water or environmental treatment, etc., are also presented. Finally, perspectives and future challenges in the field of supramolecular-macrocycle-based COMs are discussed.

Transforming Porous Organic Cages into Porous Ionic Liquids via a Supramolecular Complexation Strategy.

Porous liquids are a type of porous materials that engineer permanent porosity into unique flowing liquids, exhibiting promising functionalities for a variety of applications. Here a Type I porous liquid is synthesized by transforming porous organic cages into porous ionic liquids via a supramolecular complexation strategy. Simple physical mixing of 18-crown-6 with task-specific anionic porous organic cages affords a porous ionic liquid with anionic porous organic cages as the anionic parts and 18-crown-6/potassium ion complexes as the cationic parts. In contrast, mixing of 15-crown-5 and anionic porous organic cages in a 2:1 ratio gives only solids, while the addition of excess 15-crown-5 affords a Type II porous liquid. The permanent porosity in the cage-based porous liquids has been also confirmed by molecular simulation, positron (e+ ) annihilation lifetime spectroscopy, and enhanced gas sorption capacity compared with pure crown ethers.

A succinct strategy for construction of nanoporous ionic organic networks from a pyrylium intermediate.

Hydroxyl group and pyridinium salt-bifunctionalized nanoporous ionic organic networks prepared via a simple two-step strategy under metal- and template-free conditions are presented. The structural features of the resultant polymer (e.g. high surface area, abundant hydroxyl groups and ionic functionalities) made it a promising candidate as an efficient scavenger of toxic oxo-anions from water.

Cyclic Ether Contaminant Removal from Water Using Nonporous Adaptive Pillararene Crystals via Host-Guest Complexation at the Solid-Solution Interface.

The removal of soluble cyclic ether contaminants, such as dioxane and THF, produced in industrial chemical processes from water is of great importance for environmental protection and human health. Here we report that nonporous adaptive crystals of perethylated pillar[5]arene (EtP5) and pillar[6]arene (EtP6) work as adsorbents for cyclic ether contaminant removal via host-guest complexation at the solid-solution interface. Nonporous EtP6 crystals have the ability to adsorb dioxane from water with the formation of 1:2 host-guest complex crystals, while EtP5 crystals cannot. However, both guest-free EtP5 and EtP6 crystals remove THF from water with EtP5 having a better capacity. This is because EtP5 forms a 1:2 host-guest complex with THF via host-guest complexation at the solid-solution interface while EtP6 forms a 1:1 host-guest complex with THF. EtP6 also shows the ability to selectively remove dioxane from water even in the presence of THF. Moreover, the reversible transitions between nonporous guest-free EtP5 and EtP6 structures and guest-loaded structures make them highly recyclable.

Topotactic Synthesis of Phosphabenzene-Functionalized Porous Organic Polymers: Efficient Ligands in CO2 Conversion.

Progress toward the preparation of porous organic polymers (POPs) with task-specific functionalities has been exceedingly slow-especially where polymers containing low-oxidation phosphorus in the structure are concerned. A two-step topotactic pathway for the preparation of phosphabenzene-based POPs (Phos-POPs) under metal-free conditions is reported, without the use of unstable phosphorus-based monomers. The synthetic route allows additional functionalities to be introduced into the porous polymer framework with ease. As an example, partially fluorinated Phos-POPs (F-Phos-POPs) were obtained with a surface area of up to 591 m2 g-1 . After coordination with Ru species, a Ru/F-Phos-POPs catalyst exhibited high catalytic efficiency in the formylation of amines (turnover frequency up to 204 h-1 ) using a CO2 /H2 mixture, in comparison with the non-fluorinated analogue (43 h-1 ) and a Au/TiO2 heterogeneous catalysts reported previously (<44 h-1 ). This work describes a practical method for synthesis of porous organic phosphorus-based polymers with applications in transition-metal-based heterogeneous catalysis.

Cis-Trans Selectivity of Haloalkene Isomers in Nonporous Adaptive Pillararene Crystals.

The separation of haloalkene cis-trans isomers is difficult to achieve, yet highly desired in the chemical industry. Here, we report an energy-efficient adsorptive separation of 1,4-dichloro-2-butene (DCB) cis-trans isomers using nonporous adaptive crystals of perethylated pillararenes. Adaptive perethylated pillar[6]arene (EtP6) crystals separate the trans-DCB isomer from its cis isomer with high selectivity while perethylated pillar[5]arene (EtP5) crystals adsorb cis-trans DCB isomers without selectivity. The selectivity of EtP6 derives from the difference in the thermodynamic stabilities of guest-loaded EtP6 crystal structures upon capture of cis-trans DCB isomers, while the structural similarity of guest-loaded EtP5 leads to the loss of selectivity. EtP6 is highly recyclable due to the reversible transformations between guest-free and guest-loaded structures.

Entropy-Driven Mechanochemical Synthesis of Polymetallic Zeolitic Imidazolate Frameworks for CO2 Fixation.

High-entropy materials refer to a kind of materials in which five or more metal species were incorporated deliberately into a single lattice with random occupancy. Up to now, such a concept has been only restricted to hard materials, such as high-entropy alloys and ceramics. Herein we report the synthesis of hybrid high-entropy materials, polymetallic zeolitic imidazolate framework (also named as high-entropy zeolitic imidazolate framework, HE-ZIF), via entropy-driven room-temperature mechanochemistry. HE-ZIF contains five metals including ZnII , CoII , CdII , NiII , and CuII which are dispersed in the ZIF structure randomly. Moreover, HE-ZIF shows enhanced catalytic conversion of CO2 into carbonate compared with ZIF-8 presumably a result of the synergistic effect of the five metal ions as Lewis acid in epoxide activation.