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The applicability of allenylboronates as novel all-carbon formal 1,3-dipoles in the silver-catalysed annulation reaction with aryldiazonium salts for the synthesis of N-aryl pyrazoles is disclosed.

The dicopper site in a metal–azolate framework result in an enhanced electroreduction selectivity and current density of CO for yielding acetate.

Here, we report an improved tandem catalytic mechanism for electroreduction of CO2 to C2H4. Cu(111) nanoparticles with an average size of 5.5 ± 0.9 nm were anchored on a conductive Cu-based metal–organic framework (Cu-THQ) by in situ electrochemical synthesis. Compared to Cu(111) nanoparticles, the C2H4 faradaic efficiency of the tandem catalyst Cu(111)@Cu-THQ was increased doubly.

The photocatalytic reduction of CO2 is an effective way to solve the greenhouse effect. Different kinds of materials, such as semiconductors, coordination compounds, and bioenzymes, have been widely investigated to increase the efficiency of the photocatalytic reduction of CO2. However, a high selectivity and great stability are still challenges for material scientists. Here, we report for the first time visible light photocatalytic CO2 reduction by a series of CdSe/ZIF-8 nanocomposites combining the excellent CO2 adsorption capacity of ZIF-8 and the narrow energy gap of CdSe quantum dots (QDs). The composites show a higher catalytic performance than those of the pure components. Among CdSe/ZIF-8-x (x = nCdSe/nZIF-8), the highest yield (42.317 μmol g−1) for reducing CO2 to CO in 12 h, was obtained using nanocomposites with a ratio of 0.42 (nCdSe/nZIF-8) within the range of investigation.

Extensive efforts have been devoted to developing efficient and durable catalysts for water oxidation. Herein, we report a highly stable metal–organic framework that shows high catalytic activity and durability for electrically driven (an overpotential of 430 mV at 10 mA cm−2 in neutral aqueous solution) and photodriven (a turnover frequency of 16 s−1 and 12 000 cycles) water oxidation, representing the best catalyst for water oxidation reported to date. Computational simulation and isotope tracing experiments showed that the μ4-OH group of the {Co8(μ4-OH)6} unit participates in the water oxidation reaction to offer an oxygen vacancy site with near-optimal OH− adsorption energy.

The methylene groups surrounding the metal center in a metal–organic framework provide hydrophobic repulsive forces to H2O, resulting in a high catalytic activity (TOF = 73.8 h−1, selectivity of 96%) for photodriven CO2 reduction into CO.

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%+).

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.

By using pyridyl derivatives 4-cyanopyridine (4-pyCN) or nicotinate (na(-)) as terminal ligands (L(T)) to decorate the flexible trigonal-prismatic trinuclear metal carboxylate M3(μ3-O/μ3-OH)(RCOO)6(L(T))3 clusters, a theoretically predicted uninodal 6-connected flu-e network for [M3(μ3-O/μ3-OH)(bdc)3(L(T))3] (H2bdc = 1,4-benzenedicarboxylic acid) has been realized in three new porous coordination frameworks. The flu-e topology is isomeric to the uninodal 6-connected acs (MIL-88) and tetranodal 6-connected mtn-e (MIL-101) ones observed in the classic metal carboxylate framework materials, but comprises of unique cubic cages which require exceptional conformation for the trinuclear clusters. The weak coordinating 4-pyCN terminal ligands tend to leave the clusters during thermal activation, leading to framework distortion and reduction of the long-range order of the flu-e network, which can only be restored by 4-pyCN instead of other guest molecules. On the other hand, the carboxylate ends of the adjacent na(-) ligands coordinate with additional metal ions to crosslink the coordination networks as new binodal 4,9-connected networks with remarkably enhanced thermal/chemical stability and porosity.

Tremendous efforts have been devoted to increasing the CO2 capture performance of porous materials, especially for low CO2 concentration environments. Here, we report that hydrazine can be used as a diamine short enough to functionalize the small-pore metal–organic framework [Mg2(dobdc)] (H4dobdc = 2,5-dihydroxyl-1,4-benzenedicarboxylic acid). By virtue of the ultrahigh concentration of free amine groups (6.01 mmol g−1 or 7.08 mmol cm−3) capable of reversible carbamic acid formation, the new material [Mg2(dobdc)(N2H4)1.8] achieves a series of new records for CO2 capture, such as single-component isotherm uptakes of 3.89 mmol g−1 or 4.58 mmol cm−3 at the atmospheric CO2 concentration of 0.4 mbar at 298 K and 1.04 mmol g−1 or 1.22 mmol cm−3 at 328 K, as well as more than a 4.2 mmol g−1 or 4.9 mmol cm−3 adsorption/desorption working capacity under dynamic mixed-gas conditions with CO2 concentrations similar to those in flue gases and ambient air.

Solvothermal reactions of Co(NO3)2 with tripodal ligands 3,3′-([3,4′-bipyridine]-2′,6′-diyl)dibenzoic acid (H2L4), 3,3′-([4,4′-bipyridine]-2,6-diyl)dibenzoic acid (H2L5), and 2,6-bis(4-(1H-tetrazol-5-yl)phenyl)-4,4′-bipyridine (H2L6) possessing one to three bent arms, yielded three new porous coordination polymers, namely [Co3(μ3-OH)(L4)3] (1), [Co3(μ3-OH)(L5)3] (2), and [Co3(μ3-OH)(L6)3] (3), respectively. Single-crystal X-ray crystallography showed that 1–3 are all three-dimensional (3,9)-connected coordination networks interconnected by the tripodal ligands and the classical tricapped trigonal-prismatic [Co3(μ3-OH)(RCOO)6(Py)3] (Py = pyridyl) or new tricapped trigonal-prismatic [Co3(μ3-OH)(Rtz)6(Py)3] (Rtz− = tetrazolate) clusters. However, instead of the classical xmz topology for such a kind of 3-connected ligands and 9-connected clusters, 1 and 2 show a new (3,9)-connected topology, wys, with a point symbol of {42·6}3{46·627·83}, while 3 has a (3,9)-connected eee topology. Thermogravimetry, powder X-ray diffraction, and gas adsorption measurements demonstrated that the desolvated forms of 1–3 are all porous, but different framework flexibilities were observed.

Ethanolamine (Hea) was grafted onto the pore surface of a metal–organic framework [Zr6O4(OH)4(bdc)6] (UiO-66, H2bdc = benzene-1,4-dicarboxylic acid) by a two-step post-synthetic treatment, in which UiO-66 was first dehydrated to form [Zr6O6(bdc)6], and then reacted with Hea to form [Zr6O4(OH)2(ea)2(bdc)6] (UiO-66-EA). CO2 adsorption measurements showed that UiO-66-EA exhibits a CO2 adsorption enthalpy of 66 kJ mol−1, which is much higher than that of UiO-66 (30 kJ mol−1). Solid-state 13C NMR spectra demonstrated that carbamate species are formed by the reaction of CO2 with the amine groups in UiO-66-EA. Single-component gas adsorption measurements indicated a CO2/N2 selectivity of 365 for UiO-66-EA (15 : 75 CO2/N2 at 298 K), which is about 20 times higher than the value for UiO-66 (16). Breakthrough experiments under simulated flue gases conditions (10 : 90 CO2/N2 at 313 K) showed that the N2 purification capacity of UiO-66-EA is ca. 18 times that of UiO-66. More importantly, the breakthrough performance of UiO-66-EA can be completely maintained even at high relative humidity (82%).

We demonstrate here that porous coordination frameworks, functionalized with monodentate hydroxide on the pore surface, can achieve ultrahigh CO2 adsorption affinity (124 kJ mol−1), adsorption capacity (9.1 mmol cm−3 at 298 K and 1 bar), and CO2/N2 selectivity (262 at 298 K) by the reversible formation/decomposition of bicarbonate in the adsorption/desorption processes. More importantly, these materials can capture up to 4.1 mmol cm−3 or 13.4 wt% of CO2 from simulated flue gases (CO2 pressure 0.10–0.15 bar at 313 K) even at high relative humidity (82%) and quickly release it under mild regeneration conditions (N2 purge at 358 K), representing the best CO2 capture performances reported to date.

The solvothermal reaction of a short bridging ligand 1H-pyrazole-4-carboxylic acid (H2pc) and Zn(NO3)2 in a mixed solvent containing N,N-dimethylacetamide (DMA) at 110 °C produced two genuine supramolecular isomers [Zn2(pc)2(DMA)] (1) and [Zn2(pc)2]·DMA (2). Single-crystal X-ray diffraction studies showed that 1 is a densely packed layered structure with DMA molecules coordinated on the layered surface, and 2 is a porous three-dimensional framework structure with DMA molecules filled inside the pore without coordination to any metal ion, which represents a rare case of coordination-sphere isomerism in coordination polymers. Removal of the coordinated DMA molecules in 1 occurs at high temperatures, accompanying the irreversible formation of an unidentified nonporous phase. On the other hand, the guest DMA molecules in 2 can be readily removed under mild conditions to give a new porous phase [Zn2(pc)2] (2′). Gas-sorption measurements of 2′ revealed that the framework has significant flexibility and selective CO2 adsorption at room temperature.

Three new coordination polymers based on 4,4′-(ethyne-1,2-diyl)dibenzoic acid (H2edba) and 2,2′-bipyridine (bpy) ligands, namely, [Zn(edba)(bpy)]·xGuest (1), [Cu(edba)(bpy)]·xGuest (2), and [Co3(edba)3(bpy)2]·3DMF·H2O (3) (DMF = N,N-dimethylformamide), were synthesized under the same solvothermal conditions except for the use of different metal ions. Single-crystal X-ray analysis indicates that with the different coordination habits of Zn2+, Cu2+, and Co2+ ions, the resulting compounds feature coordination structures with different dimensionalities, namely, a 1D zigzag chain based on single-ion nodes in 1, a 2D sql layer based on dinuclear 4-connected nodes in 2, and a 3D sxb framework based on trinuclear 6-connected nodes in 3. In addition, after the removal of guest molecules, the 2D framework of 2 and the 3D framework of 3 are stable enough for CO2 sorption with Langmuir surface areas of 440 cm2 g−1 and 542 cm3 g−1, respectively. The present study serves as an example, in which the metal ion acts as the sole reaction variable, demonstrating the significance of the metal ion in the structural diversity of coordination polymers.

We show here that the interpenetration direction can be more important than the interpenetration number for the porosity, stability, framework flexibility and sorption behaviors of porous coordination frameworks. Solvothermal reactions of Zn(NO3)2 and a shape-asymmetric ligand 4-(3,5-dimethyl-1H-pyrazol-4-yl)benzoic acid (H2mpba) in different solvents/templates gave three isomeric frameworks [Zn(Hmpba)2] (1, 2, 3) possessing the same polar dia networks and 4-fold interpenetration. However, their polar nets adopt parallel, orthogonal, and anti-parallel arrangements, respectively, giving very similar voids but totally different pore shapes for 1 and 2, and a nonporous structure for 3. Thermogravimetry, powder X-ray diffraction, and sorption analyses revealed remarkably different framework flexibilities and multi-step gas sorption behavior, in which 1 selectively adsorbs CO2 over N2, 2 adsorbs both CO2 and N2, while 3 adsorbs neither CO2 nor N2. Although these compounds cannot retain their single-crystallinity after structural transformations and their complicated structures hinder conventional structural characterization techniques, we successfully combined first-principle calculations and computational simulations to solve the crystal structures of their activated phases, and developed a dynamic computational simulation method combining sorption simulated annealing, molecular mechanics and grand canonical Monte Carlo modelling to perfectly simulate the CO2 adsorption/desorption isotherms and visualize the accompanying continuous/abrupt structural transformations, demonstrating the important role of interpenetration-direction isomerism in functional porous materials.

A flexible Zn-pyrazolate-carboxylate framework [Zn7O2(deppy)2(oba)4]·2.5DMF·2H2O (1) (Hdeppy = 3,5-diethyl-4-(4′-pyridyl)pyrazole, H2oba = 4,4′-oxobisbenzoic acid) was synthesized by solvothermal reaction. Single-crystal X-ray diffraction indicated that 1 possesses a 10-connected bct topological network based on a rare heptanuclear zinc(II) cluster. Comparison of crystal structures of 1 determined at 300 K and 150 K illustrated the conformational flexibility of deppy− ligands. Thermogravimetry analyses and powder X-ray diffraction measurements showed that 1 has high thermal stability and good water stability. Gas and liquid sorption experiments of 1 not only showed stronger adsorption of CO2 compared with N2, but also demonstrated highly efficient separation of n-propylbenzene from other C9H12 alkylbenzene isomers 1,2,4-trimethylbenzene and 1,3,5-trimethylbenzene.

Solvothermal reactions of Cu(NO3)2 and 4,4′-([3,4′-bipyridine]-2′,6′-diyl)dibenzoic acid (H2L1), 3,3′-([4,4′-bipyridine]-2,6-diyl)dibenzoic acid (H2L2), or 4,4′-([4,4′-bipyridine]-2,6-diyl)dibenzoic acid (H2L3) yielded three new metal-carboxylate frameworks (MCF-28, MCF-29 and MCF-30) with a common formula [Cu2(L)2] (H2L = pyridyldicarboxylic acid). X-ray crystallography showed that MCF-28, MCF-29, and MCF-30 are three-dimensional (3,6)-connected rtl, eea and pyr networks, respectively, based on 3-connected tripodal ligands and 6-connected Cu2(RCOO)4(py)2 units (RCOO and py denote carboxylate and pyridyl groups, respectively). Thermogravimetry, powder X-ray diffraction, and gas adsorption measurements indicated that the three compounds became shrunk and amorphous structures after guest removal. Interestingly, single-crystal X-ray diffraction showed that MCF-28 exhibited drastic temperature-induced framework breathing.

Reactions of [M(NH3)2]OH (M = Ag and Cu) and 4-(1H-pyrazol-4-yl)pyridine (Hpypz), using p-xylene (C8H10) as the template, gave isomorphous two-dimensional porous metal azolate frameworks [Ag2(pypz)2]·0.5C8H10 (MAF-36(Ag), 1·g) and [Cu2(pypz)2]·0.5C8H10 (MAF-36(Cu), 2·g). Powder and single-crystal X-ray diffraction studies showed that, upon guest removal, 1·g transformed into a three-dimensional nonporous framework [Ag6(pypz)6] (1′), while 2·g can retain its porous two-dimensional structure. Depending on the metal ion, framework flexibility/rigidity, and/or porosity, 1·g and 2·g, as well as their guest-free derivatives, showed distinctly different photoluminescence and guest-responsive behaviors.

To study the potential flexibility of the (3,9)-connected xmz frameworks, a series of isoreticular metal carboxylate frameworks [M3(μ3-OH)(L)3], namely MCF-18(L,M), were constructed by 3-connected, tripodal pyridyl-dicarboxylate ligands (H2L1 = pyridine-3,5-dicarboxylic acid; H2L2 = 4,4′-(pyridine-3,5-diyl)dibenzoic acid; H2L3 = 2,6-di-p-carboxyphenyl-4,4′-bipyridine) and 9-connected, tricapped trigonal-prismatic M3(μ3-OH)(O2CR)6(py)3 (M = Fe, Co, Ni; py = pyridyl group) clusters. Powder and single-crystal X-ray diffraction studies showed that, while other isoreticular analogs do not show framework flexibility, the newly designed material MCF-18(L3,Ni) can drastically swell 70–105% in volume and 75–121% in length upon inclusion of different guests, the latter of which is the highest reported value to date. Comparison study showed that the nearly uniaxial framework breathing is generated by the special regulation effect of the xmz topology, but can only be activated by a ligand with a suitable shape. Moreover, the thermal expansion profile of MCF-18(L3,Ni) can be drastically tuned by guest, showing extremely large thermal expansion coefficients up to 430 × 10−6 K−1. The guest-included crystals also show water-like thermal expansion behaviors depending on the cooling rate, which is unanticipated for intrinsic crystalline materials.