Crystal Structure Transformation in Hydrogen-bonded Organic Frameworks via Ion Exchange

Hydrogen-bonded organic frameworks (HOFs) have emerged as rapidly growing porous materials while established permanent porosities are very fragile and difficult to stabilize due to weak hydrogen-bonding interactions among building units. Herein, we report a stable hydrogen-bonded metallotecton framework (termed as HOF-ZJU-102) that was constructed through hydrogen-bonding networks between cationic metal-organic complexes [Cu₂(Hade)₄(H₂O)₂]⁴⁺ (Hade=adenine) and GeF₆²⁻ anions. The framework not only shows permanent porosity, but also exhibits efficient separation performance of C₂H₂/C₂H₄ at room temperature. More interestingly, its crystal structure could be irreversibly transformed into isostructural counterpart HOF-ZJU-101 by ion exchange in the SiF₆²⁻ containing solution, evidenced by multiple characterization techniques including gas sorption measurements, ¹⁹F NMR spectra, FTIR and EDS. Utilizing such an ion exchange mechanism, the collapsed HOF-ZJU-102 could be restored into HOF-ZJU-101 by simply soaking in the salt solution.     

Tuning Pore Polarization to Boost Ethane/Ethylene Separation Performance in Hydrogen-Bonded Organic Frameworks

Hydrogen-bonded organic frameworks (HOFs) show great potential in energy-saving C₂H₆/C₂H₄ separation, but there are few examples of one-step acquisition of C₂H₄ from C₂H₆/C₂H₄ because it is still difficult to achieve the reverse-order adsorption of C₂H₆ and C₂H₄. In this work, we boost the C₂H₆/C₂H₄ separation performance in two graphene-sheet-like HOFs by tuning pore polarization. Upon heating, an in situ solid phase transformation can be observed from HOF-NBDA(DMA) (DMA=dimethylamine cation) to HOF-NBDA , accompanied with transformation of the electronegative skeleton into neutral one. As a result, the pore surface of HOF-NBDA has become nonpolar, which is beneficial to selectively adsorbing C₂H₆. The difference in the capacities for C₂H₆ and C₂H₄ is 23.4 cm³ g⁻¹ for HOF-NBDA , and the C₂H₆/C₂H₄ uptake ratio is 136 %, which are much higher than those for HOF-NBDA(DMA) (5.0 cm³ g⁻¹ and 108 % respectively). Practical breakthrough experiments demonstrate HOF-NBDA could produce polymer-grade C₂H₄ from C₂H₆/C₂H₄ (1/99, v/v) mixture with a high productivity of 29.2 L kg⁻¹ at 298 K, which is about five times as high as HOF-NBDA(DMA) (5.4 L kg⁻¹). In addition, in situ breakthrough experiments and theoretical calculations indicate the pore surface of HOF-NBDA is beneficial to preferentially capture C₂H₆ and thus boosts selective separation of C₂H₆/C₂H₄.     

Ortho-Alkoxy-benzamide Directed Formation of a Single Crystalline Hydrogen-bonded Crosslinked Organic Framework and Its Boron Trifluoride Uptake and Catalysis

Boron trifluoride (BF₃) is a highly corrosive gas widely used in industry. Confining BF₃ in porous materials ensures safe and convenient handling and prevents its degradation. Hence, it is highly desired to develop porous materials with high adsorption capacity, high stability, and resistance to BF₃ corrosion. Herein, we designed and synthesized a Lewis basic single-crystalline hydrogen-bond crosslinked organic framework (H_COF-50) for BF₃ storage and its application in catalysis. Specifically, we introduced self-complementary ortho-alkoxy-benzamide hydrogen-bonding moieties to direct the formation of highly organized hydrogen-bonded networks, which were subsequently photo-crosslinked to generate H_COFs. The H_COF-50 features Lewis basic thioether linkages and electron-rich pore surfaces for BF₃ uptake. As a result, H_COF-50 shows a record-high 14.2 mmol/g BF₃ uptake capacity. The BF₃ uptake in H_COF-50 is reversible, leading to the slow release of BF₃. We leveraged this property to reduce the undesirable chain transfer and termination in the cationic polymerization of vinyl ethers. Polymers with higher molecular weights and lower polydispersity were generated compared to those synthesized using BF₃ ⋅ Et₂O. The elucidation of the structure–property relationship, as provided by the single-crystal X-ray structures, combined with the high BF₃ uptake capacity and controlled sorption, highlights the molecular understanding of framework-guest interactions in addressing contemporary challenges.     

Construction of Two Stable Co(II)-Based Hydrogen-Bonded Organic Frameworks as a Luminescent Probe for Recognition of Fe3+ and Cr2O72− in H2O

A pair of cobalt(II)-based hydrogen-bonded organic frameworks (HOFs), [Co(pca)₂(bmimb)]_n (1) and [Co₂(pca)₄(bimb)₂] (2), where Hpca = p-chlorobenzoic acid, bmimb = 1,3-bis((2-methylimidazol-1-yl)methyl)benzene, and bimb = 1,4-bis(imidazol-1-ylmethyl)benzene were hydrothermally synthesized and characterized through infrared spectroscopy (IR), elemental and thermal analysis (EA), power X-ray diffraction (PXRD), and single-crystal X-ray diffraction (SCXRD) analyses. X-ray diffraction structural analysis revealed that 1 has a one-dimensional (1D) infinite chain network through the deprotonated pca⁻ monodentate chelation and with a μ₂-bmimb bridge Co(II) atom, and 2 is a binuclear Co(II) complex construction with a pair of symmetry-related pca⁻ and bimb ligands. For both 1 and 2, each cobalt atom has four coordinated twisted tetrahedral configurations with a N₂O₂ donor set. Then, 1 and 2 are further extended into three-dimensional (3D) or two-dimensional (2D) hydrogen-bonded organic frameworks through C–H···Cl interactions. Topologically, HOFs 1 and 2 can be simplified as a 4-connected qtz topology with a Schläfli symbol {6⁴·8²} and a 4-connected sql topology with a Schläfli symbol {4⁴·6²}, respectively. The fluorescent sensing application of 1 was investigated; 1 exhibits high sensitivity recognition for Fe³⁺ (K_sv: 10970 M⁻¹ and detection limit: 19 μM) and Cr₂O₇²⁻ (K_sv: 12960 M⁻¹ and detection limit: 20 μM). This work provides a feasible detection platform of HOFs for highly sensitive discrimination of Fe³⁺ and Cr₂O₇²⁻ in aqueous media.     

Efficient Trapping of Trace Acetylene from Ethylene in an Ultramicroporous Metal–Organic Framework: Synergistic Effect of High-Density Open Metal and Electronegative Sites

Acetylene (C₂H₂) removal from ethylene (C₂H₄) is a crucial step in the production of polymer-grade C₂H₄ but remains a daunting challenge because of the similar physicochemical properties of C₂H₂ and C₂H₄. Currently energy-intensive cryogenic distillation processes are used to separate the two gases industrially. A robust ultramicroporous metal–organic framework (MOF), Ni₃(pzdc)₂(7 Hade)₂, is reported for efficient C₂H₂/C₂H₄ separation. The MOF comprises hydrogen-bonded linked one-dimensional (1D) chains, and features high-density open metal sites (2.7 nm⁻³) and electronegative oxygen and nitrogen sites arranged on the pore surface as cooperative binding sites. Theoretical calculations, in situ powder X-ray diffraction and Fourier-transform infrared spectroscopy revealed a synergistic adsorption mechanism. The MOF possesses S-shaped 1D pore channels that efficiently trap trace C₂H₂ at 0.01 bar with a high C₂H₂ uptake of 60.6 cm³ cm⁻³ and C₂H₂/C₂H₄ selectivity.     

Functional self-assembly of hydrogen-bonded 3D coordination networks constructed from 1,2,4,5-benzenetetracarboxylic acid

Hydrothermal synthesis, characterization (IR, TG/DTA, element analysis, inductively coupled plasma (ICP)) and single-crystal X-ray structures of H₄Btec hydrate and its two cobalt complexes, colorless [H₄Btec · 2H₂O] _n (I), pink [Co(H₂O)₆(H₂Btec)] _n (II), and nacarat {[Co(H₂O)₃(H₂Btec)(Phen)] · H₂O} _n (III) (H₄Btec = 1,2,4,5-benzenetetracarboxylic acid, Phen = 1,10-phenanthroline) have been solved. The results showed that I forms a 3D O-H⋯O hydrogen-bonded network generated from H₄Btec and water molecules, II presents a 3D network constructed by mononuclear [Co(H₂O)₆]²⁺ cations and H₂Btec²⁻ dianions through extensive hydrogen-bonding interactions, and III gives rise to a pseudo-octahedral coordination geometry. Extensive hydrogen-bonding interactions have significant effects in configuring a 3D network constructed by mononuclear [Co(H₂Btec)(Phen)(H₂O)₃] neutral molecules and a water molecules. The article was submitted by the authors in English.     

A cobalt(II) coordination polymer with mixed 4-(5-mercapto-1H-tetrazol-1-yl)benzoate and 4,4′-bipyridine ligands: synthesis,crystal structure,and magnetic properties

A Co^II coordination polymer, {[Co(L)(bipy)(H₂O)₂](H₂O)₂}_∞ (1), with 4-(5-mercapto-1H-tetrazol-1-yl)benzoate (L) and 4,4′-bipyridine (bipy), was synthesized and structurally characterized by single-crystal X-ray diffraction analysis. Complex 1 has a (4,4) 2-D network structure, which is further interlinked by inter-layer O–H ··· O hydrogen-bonding interactions to form a 2-fold interpenetrated binodal (3,5)-connected 3-D hydrogen-bonded (6³)(6⁸ · 8²) topology. The magnetic properties of 1 feature weak antiferromagnetic coupling.     

Gradual evolution of hydrogen-bonding patterns with the carbamoylcyanonitrosomethanide anion in a series of aliphatic diammonium salts

Developing the structures of organic materials that rely on the hydrogen bonding of multifunctional substrates is often complicated due to a competition between various possible motifs. In this context, the illustrative case of the carbamoylcyanonitrosomethanide anion, [ONC(CN)–C(O)NH₂]⁻, suggests sufficient control over the crystal lattice with a set of supramolecular synthons, which are specific to all the present nitroso, carbamoyl and cyano groups. The structures of the carbamoylcyanonitrosomethanide salts of ethane-1,2-diammonium, C₂H₁₀N₂²⁺·2C₃H₂N₃O₂⁻, (1), piperazine-1,4-diium, C₄H₁₂N₂²⁺·2C₃H₂N₃O₂⁻, (2), butane-1,4-diammonium, C₄H₁₄N₂²⁺·2C₃H₂N₃O₂⁻, (3), and hexane-1,6-diammonium, C₆H₁₈N₂²⁺·2C₃H₂N₃O₂⁻, (4), reveal two- and three-dimensional hydrogen-bonded frameworks governed by a set of site-selective interactions. The strongest N—H…O hydrogen bonds [N…O = 2.6842 (17)–2.8718 (17) Å, mean 2.776 (2) Å] are associated with the polarized ammonium N—H donors and nitroso O-atom acceptors, which sustain invariant motifs in the form of nitroso/ammonium dimers. Subtle structural changes within this series of compounds concern the rupture of some weaker interactions, i.e. mutual hydrogen bonds of the carbamoyl groups in (1)–(3) [N…O = 2.910 (2)–2.9909 (18) Å; mean 2.950 (2) Å] and carbamoyl/nitrile hydrogen bonds in (1), (2) and (4) [N…N = 2.936 (2)–3.003 (3) Å, mean 2.977 (2) Å], providing a gradual evolution of the hydrogen-bonding pattern. A hierarchy of the synthons involving three different groups could be applicable to supramolecular synthesis with polyfunctional methanide species, suggesting also a degree of control over layered and interpenetrated hydrogen-bonded networks.     

Structure and fragmentation of [C3H7O]+ ions formed by chemical ionization

The unimolecular metastable and collision-induced fragmentation reactions of [C₃H₇O]⁺ ions produced by gas-phase protonation of acetone, propanal, propylene oxide, oxetan and allyl alcohol have been studied. The CID studies show that protonation of acetone and allyl alcohol yield different stable ions with distinct structures while protonation of propanal or propylene oxide yield [C₃H₇O]⁺ ions of the same structure. Protonated oxetan rearranges less readily to give the same structure(s) as protonated propanal and propylene oxide. The [C₃H₇O]⁺ ions fragmenting as metastable ions after formation by CI have a higher internal energy than the same ions fragmenting after formation by EI. Deuteronation of the C₃H₆O isomers using CD₄ reagent gas shows that loss of C₂H₃D proceeds by a different mechanism than loss of C₂H₄. The results are discussed in terms of potential energy profile for the [C₃H₇O]⁺˙ system proposed earlier.     

Bis(2,2′:6′,2′′-ter­pyridine-κ3N)­manganese(II) tetra­thionate trihydrate

The structure of the title compound, [Mn(tpy)₂](S₄O₆)·3H₂O (tpy is 2,2′:6′,2′′-ter­pyridine, C₁₅H₁₁N₃), consists of monomeric [Mn(tpy)₂]²⁺ units embedded in a complex anionic network made up of tetra­thionate ions and hydration water mol­ecules connected via a complex hydrogen-bonding scheme.     

A Microporous Hydrogen Bonded Organic Framework for Highly Selective Separation of Carbon Dioxide over Acetylene

The separation of acetylene (C₂H₂) from carbon dioxide (CO₂) is a very important but challenging task due to their similar molecular dimensions and physical properties. In terms of porous adsorbents for this separation, the CO₂-selective porous materials are superior to the C₂H₂-selective ones because of the cost- and energy-efficiency but have been rarely achieved. Herein we report our unexpected discovery of the first hydrogen bonded organic framework (HOF) constructed from a simple organic linker 2,4,6-tri(1H-pyrazol-4-yl)pyridine (PYTPZ) (termed as HOF-FJU-88) as the highly CO₂-selective porous material. HOF-FJU-88 is a two-dimensional HOFs with a pore pocket of about 7.6 Å. The activated HOF-FJU-88 takes up a high amount of CO₂ (59.6 cm³ g⁻¹) at ambient conditions with the record IAST selectivity of 1894. Its high performance for the CO₂/C₂H₂ separation has been further confirmed through breakthrough experiments, in situ diffuse reflectance infrared spectroscopy and molecular simulations.     

Synthesis and structure of [Cp2Zr(OPr)(HOPr)] and its activity in the polymerisation of propene oxide

The reaction of Cp₂Zr(OPrⁱ)₂ with [H(OEt₂)₂][H₂N{B(C₆F₅)₃}₂] in dichloromethane at room temperature gives [Cp₂Zr(OPrⁱ)(HOPrⁱ)]⁺[H₂N{B(C₆F₅)₃}₂]⁻ · Et₂O in high yield. The crystal structure is reported. The complex contains a short Zr-alkoxide and a longer Zr-alcohol bond; the OH group of the coordinated isopropanol is hydrogen-bonded to a diethyl ether molecule. The complex initiates the polymerisation of propylene oxide, most probably via a cationic mechanism.     

Structures of [C3H6O]+· ions from propylene oxide and methyl-substituted 1,3-dioxolanes by photodissociation and ion/molecule reactions

Photodissociation experiments and ion/molecule reactions with pyridine and hex-1-ene show that [C₃H₆O]^+· ions from propylene oxide isomerize to the vinyl metbyl ether structure. [C₃H₆O]^+· fragment ions from methyl-substituted 1,3-dioxolanes have lower internal energies. In these cases a mixture of photodissociating ring-opened propylene oxide ions and vinyl methyl ether ions is observed.     

Optimizing Acetylene Sorption through Induced-fit Transformations in a Chemically Stable Microporous Framework

Developing practical storage technologies for acetylene (C₂H₂) is important but challenging because C₂H₂ is useful but explosive. Here, a novel metal–organic framework (MOF) ( FJI-H36 ) with adaptive channels was prepared. It can effectively capture C₂H₂ (159.9 cm³ cm⁻³) at 1 atm and 298 K, possessing a record-high storage density (561 g L⁻¹) but a very low adsorption enthalpy (28 kJ mol⁻¹) among all the reported MOFs. Structural analyses show that such excellent adsorption performance comes from the synergism of active sites, flexible framework, and matched pores; where the adsorbed-C₂H₂ can drive FJI-H36 to undergo induced-fit transformations step by step, including deformation/reconstruction of channels, contraction of pores, and transformation of active sites, finally leading to dense packing of C₂H₂. Moreover, FJI-H36 has excellent chemical stability and recyclability, and can be prepared on a large scale, enabling it as a practical adsorbent for C₂H₂. This will provide a useful strategy for developing practical and efficient adsorbents for C₂H₂ storage.     

Nickel(II) cluster‐based mixed‐cation coordination polymer synthesized from 2‐mercaptobenzoic acid and its application

High‐nuclearity metal clusters have received considerable attention not only because of their diverse architectures and topologies, but also because of their potential applications as functional materials in many fields. To explore new types of clusters and their potential applications, a new nickel(II) cluster‐based mixed‐cation coordination polymer, namely poly[hexakis[μ₄‐(2‐carboxylatophenyl)sulfanido]di‐μ₃‐chlorido‐tri‐μ₂‐hydroxido‐octanickel(II)sodium(I)], [Ni₈NaCl₂(OH)₃(C₇H₄O₂S)₆]_n, 1 , was synthesized using nickel chloride hexahydrate and mercaptobenzoic acid (H₂mba) as starting reactants under hydrothermal conditions. The material was characterized by single‐crystal X‐ray diffraction (SCXRD), Fourier transform IR spectroscopy, thermogravimetric analysis, powder X‐ray diffraction and X‐ray photoelectron spectroscopy analysis. SCXRD shows that 1 consists of a hexanuclear nickel(II) [Ni₆] cluster, dinuclear Ni^II nodes and a mononuclear Na^I node, resulting in the formation of a complex covalent three‐dimensional network. In addition, a tightly packed NiO/C&S nanocomposite is fabricated by sintering the coordination precursor at 400 °C. The uniform nanocomposite consists of NiO nanoparticles, incompletely carbonized carbon and incompletely vulcanized sulfur. When used as a supercapacitor electrode, the synthesized composite shows an extra‐long cycling stability (>5000 cycles) during the charge/discharge process.     

Molecular Sieving of C2-C3 Alkene from Alkyne with Tuned Threshold Pressure in Robust Layered Metal–Organic Frameworks

C₂-C₃ alkyne/alkene separation is of great importance; however, designing materials for an efficient molecular sieving of alkenes from alkynes remains challenging. Now, two hydrolytically stable layered MOFs, [Cu(dps)₂(GeF₆)] (GeFSIX-dps-Cu, dps=4,4′-dipyridylsulfide) and [Zn(dps)₂(GeF₆)] (GeFSIX-dps-Zn), can achieve almost complete exclusion of both C₃H₆ and C₂H₄ from their alkyne analogues. GeFSIX-dps-Cu displays a notable advanced threshold pressure for alkynes adsorption and thus substantial uptakes at lower pressures, providing record C₃H₄/C₃H₆ uptake ratios and capacity-enhanced C₂H₂/C₂H₄ sieving for a wide composition range. Metal substitution (Zn to Cu) affords fine tuning of linker rotation and layer stacking, creating slightly expanded pore aperture and interlayer space coupled with multiple hydrogen-bonding sites, allowing easier entrance of alkyne while excluding alkene. Breakthrough experiments confirmed tunable sieving by these MOFs for C₃H₄/C₃H₆ and C₂H₂/C₂H₄ mixtures.     

Supramolecular Assemblies in Salts of 2,2＇-Biimidazole with 5-Sulfosalicylic Acid and 3,4,5-Trihydroxybenzoic Acid

Supramolecular assemblies of 2,2＇-biimidazole with 5-sulfosalicylic acid and 3,4,5-trihydroxybenzoic acid, have been synthesized and characterized by single-crystal X-ray diffraction methods. Both the two proton-transfer compounds of 2,2＇-biimidazole with 3-carboxy-4-hydroxybenzenesulfonic acid （5-sulfosalicylic acid, 5-SSA） [namely bis（2-（2-1H-imidazolyl）-1H-imidazolium） 4-hydroxybenzene-3-carboxylate-1-sulfonate monohydrate, 2（C6HTN4）^＋· CTH4068^2-.H2O, （Ⅰ）] and 3,4,5-trihydroxybenzoic acid [namely 2,2＇-bi-1H-imidazolium bis（3,4,5-trihydroxybenzoate） tetrahydrate, C6H8N4^2＋ ·2（C7H5O5）^-·4（H20）, （Ⅱ）] feature extensively hydrogen-bonded three-dimensional network structures having significant interlayer n-n interactions between the cation and anion species. In Ⅰ, a 5-SSA^2- dianionic species results from deprotonation of both the sulfonic and the carboxylic acid groups, all available O-atom acceptors interact with all cation and water molecule donors by hydrogen bonds. In Ⅱ, the formula unit displays a crystallographic inversion symmetry. The structural information about the two complexes between 2,2＇-biimidazole compound and benzenecarboxylic acids obtained in this work will be particularly important for the rational design of supramolecular organic functional materials.     

Hydro­gen bonds in the framework of bis{2-[bis(2-amino­ethyl)­amino]­ethanol}nickel(II) diperchlorate

The title molecule, [Ni(C₆H₁₇N₃O)₂](ClO₄)₂, possesses a crystallographic centre of symmetry at the Ni^II position. The coordination geometry around the Ni^II atom is distorted octahedral, consisting of six N atoms from two tripodal poly­amine ligands, while the ethanol O atoms of the ligands remain uncoordinated. The crystal packing shows two-dimensional layers and an infinite three-dimensional framework which is stabilized by a hydrogen-bonded network.     

Permeation and separation properties of polyimide membranes to olefins and paraffins

Pure and mixed gas permeation experiments for olefins and paraffins of C₂ and C₃ were carried out for several polyimide and other polymer membranes at pressures up to 8 atm and temperatures from 308 to 423 K. The olefins were more permeable to the corresponding paraffins due to their preferential diffusion based on the difference in their molecular size. Polyimide prepared from 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 2,4,6-trimethyl-1,3-phenylenediamine (TrMPD) displayed relatively high performance: permeability coefficient to propylene, P_C3H6 = 20–40 Barrer (1 Barrer = 1 × 10⁻¹⁰ cm³(STP)/(cm s cmHg)) and ideal separation factor (permeability ratio of pure propylene and propane). α_id(C₃H₆/C₃H₈) = 11 at 323 K and 2 atm. Polyimide from 6FDA and dimethyl-3,7-diaminodiphenylthiophene-5,5-dioxide (DDBT) displayed low permeability and high permselectivity: P_C3H6 = 0.8 Barrer and α_id(C₃H₆/C₃H₈) = 27 at 323 K and 2 atm. Their performance was much better than that of other polymers such as poly(2,6-dimethyl-1,4-phenyleneoxide). For mixed gas permeation, the separation factor was lower by about 40% than the α_id due to the increase in P_C3H8 caused by coexisting propylene.     

Ultrafast Semi-Solid Processing of Highly Durable ZIF-8 Membranes for Propylene/Propane Separation

ZIF-8 membranes have emerged as the most promising candidate for propylene/propane (C₃H₆/C₃H₈) separation through its precise molecular sieving characteristics. The poor reproducibility and durability, and high cost, thus far hinder the scalable synthesis and industrial application of ZIF-8 membranes. Herein, we report a semi-solid process featuring ultrafast and high-yield synthesis, and outstanding scalability for reproducible fabrication of ZIF-8 membranes. The membranes show excellent C₃H₆/C₃H₈ separation performance in a wide temperature and pressure range, and remarkable stability over 6 months. The ZIF-8 membrane features dimethylacetamide entrapped ZIF-8 crystals retaining the same diffusion characteristics but offering enhanced adsorptive selectivity for C₃H₆/C₃H₈. The ZIF-8 membrane was prepared on a commercial flat-sheet ceramic substrate. A prototypical plate-and-frame membrane module with an effective membrane area of about 300 cm² was used for efficient C₃H₆/C₃H₈ separation.