Search

Controlling interpenetration and flexibility behaviors is intriguing and fundamental for porous coordination polymers. We report exceptional interpenetration behaviors involving controllable partia...

ConspectusChemical separations, mostly based on heat-driven techniques such as distillation, account for a large portion of the world's energy consumption. In principle, differential adsorption is a more energy-efficient separation method, but conventional adsorbent materials are still not effective for many industry-relevant mixtures. Porous coordination polymers (PCPs), or metal-organic frameworks (MOFs), are attractive for their well-defined, designable, modifiable, and flexible structures connecting to various potential applications. While the importance of the structural flexibility of MOFs in adsorption-based functions has been demonstrated, the understanding of this special feature is still in its infancy and mostly stays at the periodic structural transformation at the equilibrium state and the special shapes of single-component adsorption isotherms. There are many confusions about the categorization and roles of various types of flexibility. This Account discusses the role of flexibility of MOFs for adsorptive separation, mainly from the thermodynamic and kinetic points of view.As the classic type of framework flexibility, guest-driven structural transformations and the corresponding adsorption isotherms can be thermodynamically described by the energies of the host-guest system. The highly guest-specific pore-opening action showing contrasting single-component adsorption isotherms is regarded as a strategy for achieving molecular sieving without the need for aperture size control, but its effect and role for mixture separation are still controversial. Quantitative mixture adsorption/separation experiments showed that the common periodic (cooperative) pore-opening action leads to coadsorption of molecules smaller than the opened aperture, while the aperiodic (noncooperative) one can achieve inversed molecular sieving under a thermodynamic mechanism.The energy barrier and structure in the nonequilibrium state are also important for flexibility and adsorption/separation. With suitable energy barriers between metastable structures, new types of framework flexibility such as aperture gating can be realized. While kinetically controlled gating flexibility is usually ignored because of the difficulty of characterization or considered as disadvantageous for separation because of the variable aperture size, it plays a critical role in most kinetic separation systems, including adsorbents conventionally regarded as rigid. With the concept of gating flexibility, the meanings of aperture and guest sizes for judging molecular sieving need to be reconsidered. Gating flexibility depends on not only the host itself but also the guest, the host-guest interaction, and the external environment such as temperature, which can be rationally tuned to achieve special adsorption/separation behaviors such as inversed temperature dependence, molecular sieving, and even inversed thermodynamic selectivity. The comprehensive understanding of the thermodynamic and kinetic bases of flexibility will give a new horizon for next-generation separation materials beyond MOFs and adsorbents.

A solvothermal reaction of Zn(NO3)2 and 4-(1H-pyrazol-4-yl)benzoic acid (H2pba) with toluene (Tol) as the template yielded a porous coordination polymer, [Zn(pba)]·0.5Tol, possessing a three-dimensional (3D) fence-like coordination framework based on inclined two-dimensional (2D) fence-like coordination layers. By virtue of the classic deformation mode of the 2D/3D fence structures, the guest-free structure exhibits very large positive thermal expansion of 347 MK-1 and moderate negative thermal expansion of -63/-83 MK-1, which are remarkably enhanced to new records of 689 and -171/-249 MK-1, respectively, by inclusion of Tol.

Summary The role of adsorbent flexibility for adsorptive separation is controversial. Here, we show that the gating action, an unconventional type of flexibility, can be used to achieve molecular sieving. Two isostructural metal-organic frameworks possessing quasi-discrete/gating pores are designed and synthesized, which allow CO2 adsorption from extremely low pressures. Adding amino group on the organic ligand strengthens intra-framework hydrogen bonding, which increases the gating energy barrier to completely block N2 and CH4 with larger sizes, giving record-high CO2/N2 and CO2/CH4 selectivities. C2 and C3 hydrocarbons larger than the pore induce pore opening at significantly different pressures implying C2H4/C2H6 and C3H6/C3H8 molecular sieving. Quantitative mixture breakthrough experiments show CO2/N2 and CO2/CH4 molecular sieving and the first example of switchable C2H4/C2H6 adsorption preference, but reveal C3H6/C3H8 co-adsorption. Computational simulation and in situ single-crystal/powder X-ray diffraction show that the absence and presence of pore opening are responsible for molecular sieving and co-adsorption, respectively.

Rational manipulation of supramolecular structures on surfaces is of great importance and challenging. We show that imidazole-based hydrogen-bonded networks on a metal surface can transform into an isostructural coordination network for facile tuning of the pore size and guest recognition behaviours. Deposition of triangular-shaped benzotrisimidazole (H3btim) molecules on Au(111)/Ag(111) surfaces gives honeycomb networks linked by double N–H⋯N hydrogen bonds. While the H3btim hydrogen-bonded networks on Au(111) evaporate above 453 K, those on Ag(111) transform into isostructural [Ag3(btim)] coordination networks based on double N–Ag–N bonds at 423 K, by virtue of the unconventional metal–acid replacement reaction (Ag reduces H+). The transformation expands the pore diameter of the honeycomb networks from 3.8 Å to 6.9 Å, giving remarkably different host–guest recognition behaviours for fullerene and ferrocene molecules based on the size compatibility mechanism., A hydrogen-bonded network on a Ag(111) surface can transform into an isostructural Ag(i) coordination network, giving drastically different host–guest recognition behaviours.

Porous molecular crystals sustained by hydrogen bonds and/or weaker connections are an intriguing type of adsorbents, but they rarely demonstrate efficient adsorptive separation because of poor structural robustness and tailorability. Herein, we report a porous molecular crystal based on hydrogen-bonded cyclic dinuclear AgI complex, which exhibits exceptional hydrophobicity with a water contact angle of 134°, and high chemical stability in water at pH 2-13. The seemingly rigid adsorbent shows a pore-opening or nonporous-to-porous type butane adsorption isotherm and complete exclusion of isobutane, indicating potential molecular sieving. Quantitative column breakthrough experiments show slight co-adsorption of isobutane with an experimental butane/isobutane selectivity of 23, and isobutane can be purified more efficiently than for butane. In situ powder/single-crystal X-ray diffraction and computational simulations reveal that a trivial guest-induced structural transformation plays a critical role.

Pillared-layer structures are classic for porous coordination polymers (PCPs), but suitable metal–ligand layers for such structures are rare. Here, we report a cationic {Zn2(pzdc)}+ (H3pzdc = 3,5-p...

Solvothermal reactions of 3-(3-methylpyridin-4-yl)benzoic acid (Hmpba) with Mn(NO3)2 or Co(NO3)2 yielded isostructural porous coordination polymers, [Mn(mpba)2]·guest (MCF-56, 1·g) and [Co(mpba)2]·...

Solvothermal reactions of 3-(3-methylpyridin-4-yl)benzoic acid (Hmpba) with Zn(II), Cd(II), or Cu(II) salts yielded crystals of coordination polymers [Zn(mpba)2] (1), [Cd(mpba)2] (2), and [Cu(mpba)2]·guest (3·g), respectively, possessing two-dimensional (2D) 4-connected sql coordination networks with different packing/interpenetration modes. 1 and 2 both possess close-packing two-fold interpenetrated sql nets, but the ligand orientations in their single layers and the stacking manners of their double layers are quite different and have an inversed trend of complexity. The sql nets in 3 are non-interpenetrated, which loosely pack to give a porous structure with 1D channels. Interestingly, 1–3 have a completely inversed trend in packing/interpenetration and porosity, compared to the coordination networks constructed by the same metal ions and the ligand without the methyl group (3-(pyridin-4-yl)benzoic acid). The porous framework of 3 can be retained after guest removal, as demonstrated by the CO2 adsorption isotherms and high catalytic performances for cycloaddition of epoxides and CO2.

Molecular sieving can lead to ultrahigh selectivity and low regeneration energy because it completely excludes all larger molecules via a size restriction mechanism. However, it allows adsorption of all molecules smaller than the pore aperture and so separations of complicated mixtures can be hindered. Here, we report an intermediate-sized molecular sieving (iSMS) effect in a metal-organic framework (MAF-41) designed with restricted flexibility, which also exhibits superhydrophobicity and ultrahigh thermal/chemical stabilities. Single-component isotherms and computational simulations show adsorption of styrene but complete exclusion of the larger analogue ethylbenzene (because it exceeds the maximal aperture size) and smaller toluene/benzene molecules that have insufficient adsorption energy to open the cavity. Mixture adsorption experiments show a high styrene selectivity of 1,250 for an ethylbenzene/styrene mixture and 3,300 for an ethylbenzene/styrene/toluene/benzene mixture (orders of magnitude higher than previous reports). This produces styrene with a purity of 99.9%+ in a single adsorption-desorption cycle. Controlling/restricting flexibility is the key for iSMS and can be a promising strategy for discovering other exceptional properties.

Efficient adsorptive separation of propylene/propane (C3 H6 /C3 H8 ) is highly desired and challenging. Known strategies focus on either the thermodynamic or the kinetic mechanism. Here, we report an interesting reactivity of a metal-organic framework that improves thermodynamic and kinetic adsorption selectivity simultaneously. When the metal-organic framework is heated under oxygen flow, half of the soft methylene bridges of the organic ligands are selectively oxidized to form the more polar and rigid carbonyl bridges. Mixture breakthrough experiments showed drastic increase of C3 H6 /C3 H8 selectivity from 1.5 to 15. For comparison, the C3 H6 /C3 H8 selectivities of the best-performing metal-organic frameworks Co-MOF-74 and KAUST-7 were experimentally determined to be 6.5 and 12, respectively. Gas adsorption isotherms/kinetics, single-crystal X-ray diffraction, and computational simulations revealed that the oxidation gives additional guest recognition sites, which improve thermodynamic selectivity, and reduces the framework flexibility, which generate kinetic selectivity.

Metal-organic frameworks (MOFs) for enzyme immobilization have already shown superior tunable and designable characteristics, however, their diverse responsive properties have rarely been exploited. In this work we integrated a responsive MOF into a MOF-enzyme composite with the purpose of designing an "all-in-one" multifunctional composite with catalytic and luminescence functions incorporated into a single particle. As a proof-of-concept, glucose oxidase (GOx) was encapsulated in situ within an oxygen (O2 )-sensitive, noble-metal-free, luminescent CuI triazolate framework (MAF-2), denoted as GOx@MAF-2. Owing to the rigid scaffold of MAF-2 and confinement effect, the GOx@MAF-2 composite showed significantly improved stability (shelf life of 60 days and heat resistance up to 80 °C) as well as good selectivity and recyclability. More importantly, owing to the O2 sensitivity of MAF-2, the GOx@MAF-2 composite exhibited a rapid and reversible response towards dissolved O2 , thereby allowing direct and ratiometric sensing of glucose without the need for chromogenic substrates, cascade enzymatic reactions, or electrode systems. High sensitivity with a detection limit of 1.4 μm glucose was achieved, and the glucose levels in human sera were accurately determined. This strategy has led to a new application for MOFs that can be facilely extended to other MOF-enzyme composites due to the multifunctionality of MOFs.

A rhombic porous coordination polymer was synthesized as two conformational isomers with acute and obtuse interior angles, which can reversibly and irreversibly transform into a new conformation, undergoing not only single-side but also double-side swing.

Hydrophobic ethyl, butyl or hexyl groups were introduced into the dicarboxylate ligand in the fluorescent porous coordination framework [Zn2(fda)2(bpy)] (LMOF-202, H2fda=9 H -fluorene-2,7-dicarboxylic acid, bpy=4,4′-bipyridine) for improving water stability and tuning oxygen sensitivity. The long hexyl groups gave satisfactory water stability but its oxygen sensitivity is low (70.8% fluorescence quenched at 1 bar O2 (1 bar = 105 Pa)). In contrast, the shorter side groups gave high oxygen sensitivity (93.9% fluorescence quenched at 1 bar O2) and low water stability. The derivation of the Stern-Volmer curves of the O2 luminescence quenching data from the linear form can be used for detecting trace impurities in the luminescent framework, being much more sensitive than conventional methods such as powder X-ray diffraction. Mixing the ethyl and hexyl groups in the solid-solution manner brought high oxygen sensitivity (96.4% fluorescence quenched at 1 bar O2) and high water stability simultaneously in the same coordination framework.

3-Ethyl-5-trifluoromethyl-1,2,4-triazole is synthesized by a one-pot reaction. Using this asymmetric triazole ligand bearing one trifluoromethyl and one ethyl as side groups, we construct two new porous coordination polymers, MAF-9 and MAF-2F, being isostructural with the classic hydrophobic and flexible materials, FMOF-1 and MAF-2, based on symmetric triazole ligands bearing two trifluoromethyl groups or two ethyl groups, respectively. MAF-9 and MAF-2F can adsorb large amounts of organic solvents but completely exclude water, showing superhydrophobicity with water contact angles of 152o in between those of FMOF-1 and MAF-2. MAF-9 exhibits very large N2-induced breathing and colossal positive and negative thermal expansions like FMOF-1, but the lower molecular weight and smaller volume of MAF-9 give 16% and 4% higher gravimetric and volumetric N2 uptakes, respectively. In contrast, MAF-2F is quite rigid and does not show the inversed temperature-dependent N2 adsorption and large guest-induced expansion like MAF-2. Further, despite the higher molecular weight and larger volume, MAF-2F possesses 6% and 25% higher gravimetric and volumetric CO2 uptakes, respectively. These results can be explained by the different pore sizes and side group arrangements in the two classic framework prototypes, which demonstrate the delicate roles of ligand side groups in controlling porosity, surface characteristic and flexibility., By partial replacement of the non-coordinative ligand side groups, the classic porous framework materials can be easily synthesized with their main adsorption properties retained or even improved.

Porous coordination polymers (PCPs) or metal–organic frameworks (MOFs) have been widely used as catalysts for their large porosities, uniform pore sizes/shapes, diversified/tunable pore surfaces, redox properties, and other unique structural features. Accompanying the urgent need for clean and sustainable technologies for energy storage and conversion, as well as the fast improvement of the chemical stability of these materials, MOFs and their composites are emerging as unique electrocatalysts for the hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, carbon dioxide reduction reaction, and some other redox reactions. This review summaries representative progress and focuses on the structure–property relationships. Combining the advantages of inorganic heterogeneous and molecular homogeneous catalysts, MOFs can serve as a promising platform for achieving high electrocatalytic performances and studying the electrocatalytic mechanisms. More attention should be devoted to designing new MOFs with high chemical stability and electric conductivity, and optimizing their crystal growth on conducting substances.

Active DNA demethylation, mediated by O2-dependent ten–eleven translocation (TET) enzymes, has essential roles in regulating gene expression. TET kinetics assay is vital for revealing mechanisms of demethylation process. Here, by a metal–organic framework (MOF)-based optical O2 sensor, we present the first demonstration on real-time TET2 kinetics assay in vitro. A series of luminescent Cu(I) dialkyl-1,2,4-triazolate MOFs were synthesized, which were noble-metal-free and able to intuitively response to dissolved O2 in a wide range from cellular hypoxia (≤15 μM) to ambient condition (∼257 μM). By further immobilization of the MOFs onto transparent silicon rubber (MOF@SR) to construct O2 film sensors, and real-time monitoring of O2 consumption on MOF@SR over the reaction time, the complete TET2-mediated 5-methylcytosine (5mC) oxidation process were achieved. The method overcomes the limitations of the current off-line methods by considerably shortening the analytical time from 0.5–18 h to 10 min, and remarka...

Membrane separation is a cost-effective and energy-saving technology compared with physical adsorption, chemical absorption, distillation, and other conventional methods. With high surface area, uniform and adjustable pore aperture size/shape, etc., porous coordination polymers or metal-organic frameworks (MOFs) have demonstrated outstanding potentials for storage, separation, catalysis, sensing and many other applications. MOFs are also emerging as promising membrane materials in recent years. Nevertheless, most MOF-based membranes still suffer from complicated synthesis, low stability, low permeability, and/or low selectivity. SOD-[Zn(mim)2] (MAF-4 or ZIF-8, Hmim=2-methylimidazole) with a very small aperture size (0.34 nm) is a zeolitic MOF material having high chemical stability and thermal stability. Besides adsorption, catalysis, and many other functions, MAF-4 has also been extensively studied as a membrane material, and many membrane synthesis methods and membrane supports have been reported. As a Zn(II)-based MOF, MAF-4 crystals/membranes can grow on ZnO surface by partial conversion of the oxide to the MOF component. Therefore, porous ZnO may be a suitable support for a MAF-4 membrane. However, for known MAF-4 membrane synthesis methods, the ZnO layers need to be coated on the surface of conventional supports such as porous α-Al2O3, silica, and titania, by complicated procedures. To utilize the advantage of ZnO and simplify the membrane preparation process, porous ZnO supports were used in this work, and MAF-4 membranes were successfully grown by the facile secondary growth method. Powder X-ray diffraction, energy dispersive X-ray spectroscopy and scanning electron microscope showed that the obtained membranes were compact and continuous with thickness of 4 μm. Single-component gas permeation experiments gave an H2/CO2 ideal selectivity of 7.5 and an H2 permeance of 2.1×10-7 mol/(m2 Pa s) under a pressure drop of 100 kPa at 25°C. When the temperature increased to 100°C, the H2/CO2 ideal selectivity increased to 25, while the H2 permeance remained 2.0×10-7 mol/(m2 Pa s). For equimolar H2/CO2 mixture, the obtained MAF-4 membrane showed a selectivity of 5.7 for H2/CO2 and a H2 permeance of 1.2×10-7 mol/(m2 Pa s) under a pressure drop of 100 kPa at 25°C. This work indicates porous ZnO as a suitable support for fabrication of other Zn-based MOF membranes.

Solvothermal reactions of Zn(II) salts and 4-(1H-pyrazol-4-yl)pyridine (Hpypz) in the presence of monocarboxylate or dicarboxylate ligands produced two porous coordination polymers, namely, [Zn(pypz)(OAc)]·guest (1·g, HOAc = acetic acid) and [Zn2(pypz)2(oba)]·guest (2·g, H2oba = 4,4′-oxobisbenzoic acid). Single-crystal X-ray diffraction analyses showed that both 1 and 2 contain 2-fold interpenetrated three-dimensional nbo-a {Zn(pypz)}+ networks consisting of 3-connected Zn(II) ions and 3-connected pypz– ligands. After the carboxylate ligands were considered, 1 retains the nbo-a network structure and contains one-dimensional channels with very narrow apertures. On the other hand, 2 becomes a new uninodal 6-connected topology (point symbol 33.42.56.64) and contains discrete pores. Powder X-ray diffraction showed that, after solvent removal, 1 undergoes obvious framework shrinkage, while 2 retains the original unit cell. Activated 1 and 2 both exclude N2 at 77 K, but readily adsorb CO2 at 195 K with unconven...

光学陶瓷是一种透明的特种陶瓷, 可兼备单晶的高稳定性和玻璃、流体和其他非晶材料的大尺寸的优点, 是有潜力的激光增益介质. 因为对晶体尺寸和对称性有严格要求, 而且需要高温烧结过程, 只有少数无机非金属材料可用于制备光学陶瓷. 本文报道了一种由配位聚合物(或称金属—有机框架)组成的新型陶瓷. 通过简单地降低溶剂挥发速度, MAF-4(即SOD型二甲基咪唑锌, 也称ZIF-8)的纳米晶即可融合形成致密的陶瓷状块体, 甚至具有毫米级尺寸和高达84%可见光透过率. 该金属—有机光学陶瓷MOOC-1可以负载荧光染料sulforhodamine 640并保持其发光特性, 包括很高的量子产率63.6%和极低的放大自发辐射阈值31 μJ cm-2. 其他几种金属—有机框架的纳米晶也可以在类似条件下融合成陶瓷或光学陶瓷. 考虑到金属—有机框架的结构和功能多样性, 金属—有机陶瓷不但可用作光学器件, 还可能在吸附、分离、传感等相关领域展现潜力.

Controllable design and synthesis are a great challenge to the fabrication of micro-/nano-structures of electrode materials in heterogeneous electrocatalysis. Herein, by virtue of an inorganic-MOF-inorganic (IMI) two-stage precursor approach, novel ultrathin CuO decorated Cu–C hybrid nanorod arrays supported on carbon fiber cloth (CFC) have been developed as highly efficient electrocatalysts for the oxygen evolution reaction (OER), and exhibit a current density of 10 mA cm−2 at an overpotential of 340 mV in 1.0 M KOH, ranking as one of the best copper-based OER catalysts. Further experimental results indicate that the ultrathin cupric oxide overlayers and special nanorod array morphology are crucial to boosting the electrocatalytic activity, which provides a new train of thought for utilizing low-cost and eco-friendly copper-based materials in energy storage/conversion.

Solvothermal reaction of Zn(NO3)2 and a bifunctional ligand 4-(3,5-dimethyl-1H-pyrazol-4-yl)benzoic acid (H2mpba) using benzene as template gave a two-fold interpenetrated porous framework [Zn2(Hmpba)2(mpba)]·2C6H6 (1·C6H6 or MCF-54), which displayed single-crystal to single-crystal (SCSC) structural transformations upon activation and adsorption of methanol, toluene and cyclohexane. Single-crystal structural analysis and computational simulations demonstrated that compound 1 possesses adaptive pores toward various shapes or arrangements of guests. Using silicone rubber as binder, microcrystalline powders of 1 were coated on the inner surface of a capillary column for gas chromatography, which displayed high separation performances and/or abnormal separation sequences for similar benzene homologues. By virtue of the large loading amount of adsorbent, the column shows extra-large column-capacity, being almost 300 times larger than that of common commercial capillary columns, leading to good selectivities and resolutions even in the presence of large amount of interferents.

Porous materials bearing free aliphatic amine groups are powerful adsorbents for carbon dioxide but generally have to be synthesized by complicated, multi-step post-synthetic modification methods due to the high activity of these functional groups. We report a crystal-engineering strategy for such metal–organic frameworks. Reactions of Zn(II) ion with diversified coordination modes and bis(4-carboxy-benzyl)amine (H2bcba) with a secondary aliphatic amine bridge at different temperatures yielded a pair of isomeric frameworks with very similar framework structures but distinctly different local structures, namely α-[Zn(bcba)] (MCF-51 or α-Zn) with all amino groups coordinated and β-[Zn(bcba)] (MCF-52 or β-Zn) with uncoordinated amino groups. Single-component gas adsorption and CO2/CH4 mixture breakthrough experiments at ambient conditions showed that, the CO2 adsorption ability and CH4 purification performances of β-Zn, in terms of CO2 adsorption enthalpy (42 kJ mol−1), CO2/CH4 selectivity (32) and CH4 purity/productivity (1.49 mmol g−1 at 99.999%+), are much higher than those of α-Zn (CO2 adsorption enthalpy of 17 kJ mol−1, CO2/CH4 selectivity of 2.9 and CH4 purity/productivity of 0.088 mmol g−1 at 99%+).

Converting CO2 into fuels via photochemical reactions relies on highly efficient and selective catalysts. We demonstrate that the catalytic active metal center can cooperate with neighboring hydroxide ligands to boost the photocatalytic CO2 reduction. Six cobalt-based metal–organic frameworks (MOFs) with different coordination environments are studied at the same reaction condition (photosensitizer, electron donor, water/organic mixed solvent, and visible light). In pure CO2 at 1.0 atm, the MOFs bearing μ-OH– ligands neighboring the open Co centers showed CO selectivities and turnover frequencies (TOFs) up to 98.2% and 0.059 s–1, respectively. More importantly, their TOFs reduced only ca. 20% when the CO2 partial pressure was reduced to 0.1 atm, while other MOFs reduced by at least 90%. Periodic density functional theory calculations and isotope tracing experiments showed that the μ-OH– ligands serve not only as strong hydrogen-bonding donors to stabilize the initial Co–CO2 adduct but also local proton so...

Framework flexibility is one of the most important characteristics of metal-organic frameworks (MOFs), which is not only interesting, but also useful for a variety of applications. Designing, tailoring or controlling framework flexibility of MOFs is much more difficult than for static structural features such as the framework topology and pore size/shape. Nevertheless, with in-depth understanding of the relationship between framework flexibility and the host framework structure, guest loading and other aspects such as the crystal size/morphology and external physical environment, some strategies have been developed for controlling the flexibility of MOFs and the corresponding properties, which are summarized and discussed in this review.

Conventional adsorbents preferentially adsorb the small, high-polarity, and unsaturated 1,3-butadiene molecule over the other C4 hydrocarbons from which it must be separated. We show from single-crystal x-ray diffraction and computational simulation that a hydrophilic metal-organic framework, [Zn2(btm)2], where H2btm is bis(5-methyl-1H-1,2,4-triazol-3-yl)methane, has quasi-discrete pores that can induce conformational changes in the flexible guest molecules, weakening 1,3-butadiene adsorption through a large bending energy penalty. In a breakthrough operation at ambient temperature and pressure, this guest conformation-controlling adsorbent eluted 1,3-butadiene first, then butane, butene, and isobutene. Thus, 1,3-butadiene can be efficiently purified (≥99.5%) while avoiding high-temperature conditions that can lead to its undesirable polymerization.

Luminescent porous coordination polymers (PCPs) are emerging as attractive oxygen-sensing materials, but they are mostly based on single-wavelength luminometry. Here, we report a special mixed-lanthanide strategy for self-referenced ratiometric oxygen sensing. A series of isostructural, pure-lanthanide, or mixed-lanthanide PCPs, MCF-53(Tb/Eux), were synthesized by solvothermal reactions. Single-crystal X-ray diffraction revealed that MCF-53(Tb/Eux) is composed of complicated two-dimensional coordination networks, which interdigitate to form a three-dimensional supramolecular structure retaining one-dimensional ultra-micropores. MCF-53(Tb/Eux) can undergo multiple single-crystal to single-crystal structural transformations upon desorption/adsorption of coordinative and lattice guest molecules, and the lanthanide metal ions are partially exposed on the pore surface at the guest-free state. Tb(III) ions are not luminescent and only act as separators between Eu(III) ions, and the Tb(III)/Eu(III) mixing ratio can tune the relative emission intensities, luminescence lifetimes of the Eu(III) phosphorescence, and the ligand fluorescence, giving rise to not only ratiometric photoluminescence oxygen sensing but also tunable emission-color-changing ranges.

Among various types of nonporous and porous coordination polymers, and as a subset of metal azolate frameworks (MAFs), Cu(I) 1,2,4-triazolates are unique for their simple three-connected network topologies which can be controlled by their significant steric hindrance effects between the noncoordinative side groups. This perspective article discusses the crystal engineering, structures, and diversified properties of Cu(I) 1,2,4-triazolates, particularly focusing on the porous coordination polymer [Cu(detz)] (MAF-2, Hdetz = 3,5-diethyl-1,2,4-triazole) showing unique/multimode flexibility, high hydrophobicity, bright phosphorescence, and exceptionally high stabilities toward not only guest change but also water and oxygen, which have demonstrated as a good platform for realizing high-performance applications related to gas/vapor confinement, storage, separation, and sensing. The exceptional O2 reactivity and the tunable framework flexibility, pore surface polarity, and gas separation performances of [Cu4(btm...

Pyrolysis treatments of three [Zn(eim)2] (Heim = 2-ethylimidazole) supramolecular isomers, namely MAF-5 (ANA, 38.6%), MAF-6 (RHO, 55.4%) and MAF-32 (qtz, 0%), possessing different network topologies and porosities, gave morphology-retaining, nitrogen-doped porous carbons denoted as CMAF-5, CMAF-6 and CMAF-32, respectively. Elemental analyses gave nitrogen contents of CMAF-32 (5.45%) > CMAF-5 (5.05%) > CMAF-6 (2.55%), indicating that larger pores are beneficial for the removal of nitrogen contents. Ar sorption measurements for CMAF-5/CMAF-6/CMAF-32 gave pore volumes and surface areas of 0.42/0.65/0.35 cm3 g−1 and 1027/1453/730 m2 g−1, respectively, which are higher than those of their precursors but showing the same trend. The pore sizes of CMAF-5/CMAF-6/CMAF-32 mainly distribute in the ultramicroporous region of 3.7 to 7.5 A, but still follow CMAF-32 < CMAF-5 < CMAF-6, coincident with the porosities of their precursors. These carbons show remarkable CO2 sorption and CO2/N2 selectivities, consistent with their pore sizes and nitrogen contents. Notably, the IAST CO2/N2 (v/v = 15 : 85, 298 K and 1 bar) selectivities of CMAF-5 and CMAF-32 reach 180 and 262, respectively, which are the highest among all known porous carbon materials. Mixed-gas breakthrough experiments using a 15 : 85 CO2/N2 mixture gave a CO2/N2 selectivity of 234 for CMAF-32.

Reactions of a new bent dipyridyl-type ligand, 3,6-di(pyridin-4-yl)-9H-carbazole (dpc), with different Zn(II) salts yielded four coordination polymers, namely [ZnCl2(dpc)] (1), [Zn4Cl8(dpc)4]·1.44H2O (2), [ZnF(dpc)2(H2O)]PF6·2H2O·2DMF (3) (DMF = N,N-dimethylformamide), and [Zn(dpc)2(SiF6)]·guest (4). By virtue of the bent coordination geometries of both the tetrahedral Zn(II) ion and the dipyridyl ligand, as well as the termination effect of the Cl− counter-anion/ligand, 1 is a single-stranded helical chain. 2 is a supramolecular isomer of 1 containing the same bent ZnCl2(dpc) secondary building unit, but four of such units interconnect to form a molecular Mobius ring. More interestingly, the molecular Mobius rings in 2 mechanically interlock with their neighbours to form a curb chain. With weakly coordinating PF6− as a counter-anion, 3 is a cationic loop chain consisting of vertex-sharing rhombus molecular rings built from two metal ions and two organic ligands. 4 contains vertex-sharing loop chains similar to those in 3, but they are connected by SiF62− to form a neutral layered network possessing intralayer channels for gas adsorption.

Solvothermal reactions of 3-methyl-5-trifluoromethyl-1,2,4-triazole (Hfmtz) with Cu(CH3COO)2 at 120 °C in the presence of Cl- generate two partially fluorinated coordination polymers: i.e., [Cu4Cl(fmtz)3] (1 or MAF-51) and [Cu7Cl(fmtz)6] (2 or MAF-52). Single-crystal X-ray diffraction revealed 1 to have a three-dimensional (3D) nonporous structure with pcu topology consisting of 6-connected Cu4(μ4-Cl) clusters and 2 to possess a highly porous (void ratio 48%) 3D bnn network consisting of 5-connected Cu5(μ5-Cl) clusters. Benefiting from the hydrophobic pendant groups, complete coordination of the ligand N atoms, and strong M-N coordination bonds, 1 and 2 possess high water stability (exposed to water for at least 1 year) and hydrophobicity (water contact angles of 141° and 148°, respectively). The N2 sorption isotherm of activated 2 gave Langmuir/BET surface areas of 1023/848 m2 g-1 and a pore volume of 0.365 cm3 g-1. Moreover, 2 can adsorb large amounts of benzene and methanol but barely adsorb water. Both 1 and 2 show phosphorescence of Cu(I) complexes, but only that of porous 2 is sensitive to O2, showing a linear Stern-Volmer response below 1 mbar with an ultrahigh Ksv value of 5234 bar-1 and ultralow limit of detection of 1.9 ppm.

Understanding, controlling, and utilizing the flexibility of adsorbents are of great importance and difficulty. Analogous with conventional solid materials, downsizing to the nanoscale is emerging as a possible strategy for controlling the flexibility of porous coordination polymers (or metal-organic frameworks). We report a unique flexibility controllable by crystal size at the micrometer to submillimeter scale. Template removal transforms [Cu 2 (pypz) 2 ]·0.5 p -xylene (MAF-36, Hpypz = 4-(1 H -pyrazol-4-yl)pyridine) with one-dimensional channels to α -[Cu 2 (pypz) 2 ] with discrete small cavities, and further heating gives a nonporous isomer β -[Cu 2 (pypz) 2 ]. Both isomers can adsorb p -xylene to give [Cu 2 (pypz) 2 ]·0.5 p -xylene, meaning the coexistence of guest-driven flexibility and shape-memory behavior. The phase transition temperature from α -[Cu 2 (pypz) 2 ] to β -[Cu 2 (pypz) 2 ] decreased from ~270°C to ~150°C by increasing the crystal size from the micrometer to the submillimeter scale, ca. 2-3 orders larger than those of other size-dependent behaviors. Single-crystal X-ray diffraction showed coordination bond reconstitution and chirality inversion mechanisms for the phase transition, which provides a sufficiently high energy barrier to stabilize the metastable phase without the need of downsizing to the nanoscale. By virtue of the crystalline molecular imprinting and gate-opening effects, α -[Cu 2 (pypz) 2 ] and β -[Cu 2 (pypz) 2 ] show unprecedentedly high p -xylene selectivities of 16 and 51, respectively, as well as ultrafast adsorption kinetics (

Behaving as structural protectors and electronic modulators, catalyst supports such as graphene derivatives are generally constructed by covalent bonds. Here, hydrogen-bonded ultrathin nanosheets are reported as a new type of catalyst support. Melamine (M) and cyanuric acid (CA) molecules self-assemble to form the graphite-like hydrogen-bonded co-crystal M-CA, which can be easily exfoliated by ultrasonic treatment to yield ultrathin nanosheets with thickness of ≈1.6 nm and high stability at pH = 0. The dynamic nanosheets form adaptive defects/pores in the synthetic process of CoP nanoparticles, giving embedded composite with high hydrogen evolution activity (overpotential of 66 mV at 10 mA cm-2 ) and stability. Computational calculations, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy unveil the electron modulation effects of the nanosheets. This pseudo-porous catalyst support also can be applied to other metal phosphides.

Gene silencing holds promise for cancer therapeutics because of its potential to inhibit genes involved in tumor development. However, gene silencing is still restricted by its limited efficacy and safety. Nanoscale coordination polymers (CPs) emerge as promising nanocarriers for gene delivery, but their responsiveness and potential therapeutic properties have rarely been explored simultaneously. Here, multifunctional ultrathin 2D nanosheets of Cu(I) 1,2,4-triazolate CP with a thickness of 4.5 ± 0.8 nm are synthesized using a bottom-up method. These CP nanosheets can act as both an effective DNAzyme nanocarrier for gene therapy and an intrinsic photosensitizer for hypoxia-tolerant type I photodynamic therapy (PDT), which is ascribed to the Fenton-like reaction. Because of the glutathione (GSH)-responsiveness of the CP nanosheets, DNAzyme-loaded CP nanosheets exhibit excellent cancer-cell-targeting gene silencing of the early growth response factor-1 (EGR-1), with messenger RNA inhibited by 84% in MCF-7 (human breast cancer cells) and only 6% in MCF-10A (normal human mammary epithelial cells). After tail intravenous injection into MCF-7-tumor-bearing mice, the CP nanosheets loaded with chlorin-e6-modified DNAzyme under photoirradiation show a high antitumor efficacy (88.0% tumor regression), demonstrating a promising therapeutic platform with efficient and selective gene silencing and PDT of cancer.

Mixing molecular building blocks in the solid solution manner is a valuable strategy to obtain structures and properties in between the isostructural parent metal–organic frameworks (MOFs). We report nonlinear/synergistic solid-solution effects using highly related yet non-isostructural, phosphorescent CuI triazolate frameworks as parent phases. Near the phase boundaries associated with conformational diversity and ligand heterogeneity, the porosity (+150 %) and optical O2 sensitivity (410 times, limit of detection 0.07 ppm) can be drastically improved from the best-performing parent MOFs and even exceeds the records hold by precious-metal complexes (3 ppm) and C70 (0.2 ppm).

Postsynthetic ion exchange of [Co2(μ-Cl)2(btta)] (MAF-X27-Cl, H2bbta =1H,5H-benzo(1,2-d:4,5-d')bistriazole) possessing open metal sites on its pore surface yields a material [Co2(μ-OH)2(bbta)] (MAF-X27-OH) functionalized by both open metal sites and hydroxide ligands, giving drastically improved electrocatalytic activities for the oxygen evolution reaction (an overpotential of 292 mV at 10.0 mA cm(-2) in 1.0 M KOH solution). Isotope tracing experiments further confirm that the hydroxide ligands are involved in the OER process to provide a low-energy intraframework coupling pathway.