Porous Coordination Framework Research Articles

Tuning oxygen-sensing behaviour of a porous coordination framework by a guest fluorophore

A new oxygen-sensing material with desirable excitation/emission characteristics was achieved by using a simple guest fluorophore.

Tuning fluorocarbon adsorption in new isoreticular porous coordination frameworks for heat transformation applications.

Adsorption heat transformation is one of the most energy-efficient technologies, which relies much on the type and performance of the adsorbent-adsorbate pair. Here, we report adsorption behaviors of a typical fluorocarbon R22 (CHClF2) in a new series of isoreticular porous coordination polymers [Zn4O(bpz)2(ldc)], in which the typical Zn4O clusters are connected by hydrophobic 3,3',5,5'-tetramethyl-4,4'-bipyrazolate (bpz2-) and different linear dicarboxylates (ldc2-) to form non-interpenetrated pcu networks with variable pore sizes, shapes, and volumes. Fluorocarbon sorption measurements of these materials revealed high R22 uptakes of 0.73-0.97 g g-1 (0.62-0.65 g cm-3) at 298 K and 1 bar and working capacities of 0.41-0.72 g g-1 (0.35-0.47 g cm-3) between 273 and 313 K at about 0.13, 0.11 and 0.52 bar, respectively, as well as very large diffusion coefficients of 5.1-7.3 × 10-7 cm2 s-1. Noteworthily, the R22 sorption performance can be dramatically improved by subtle modification of the pore size and shape, demonstrating porous coordination polymer-fluorocarbon as a promising adsorbent-adsorbate pair for heat transformation applications.

Visualizing the distinctly different crystal-to-crystal structural dynamism and sorption behavior of interpenetration-direction isomeric coordination networks

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.

ChemInform Abstract: Control over Flexibility of Entangled Porous Coordination Frameworks by Molecular and Mesoscopic Chemistries

AbstractReview: [28 refs.

Ionic liquids used for synthesis of supramolecular isomeric open-frameworks as photocatalysts for visible-light-driven degradation of organic dyes

Two supramolecular isomeric anionic porous coordination frameworks synthesised using ion liquids contain similar linear trinuclear zinc motifs but exhibit quite different (4,7)- and (4,6)-connected topologies. Isomer 1 can degrade methylene blue (MB) effectively under UV-light-irradiation, but isomer 2 showed remarkable visible-light-driven degradation of diverse organic dyes.

A Noble‐Metal‐Free Porous Coordination Framework with Exceptional Sensing Efficiency for Oxygen

Light material: By virtue of the unique framework structure and very high oxygen permeability, a noble-metal-free, highly fluorescent, porous coordination polymer demonstrates a rapid, reversible, efficient, stable, and selective fluorescence-quenching response toward oxygen. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

A Noble‐Metal‐Free Porous Coordination Framework with Exceptional Sensing Efficiency for Oxygen

A Noble‐Metal‐Free Porous Coordination Framework with Exceptional Sensing Efficiency for Oxygen

Control over Flexibility of Entangled Porous Coordination Frameworks by Molecular and Mesoscopic Chemistries

Abstract Entangled porous coordination frameworks, wherein two or more distinct frameworks are catenated over an entire crystal, are known to demonstrate unique structural flexibilities in response to the accommodation of molecules in the voids between the frameworks. In this highlight review, we introduce key functions of entangled frameworks based on two principles of their dynamic features: shearing and displacement. We further describe strategies to control the flexibilities; one is a molecular chemistry approach to functionalize frameworks by chemical modification, and the other is a mesoscopic chemistry approach to change the physical form, in particular, the crystal size.

Turning on the flexibility of isoreticular porous coordination frameworks for drastically tunable framework breathing and thermal expansion

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.

A porous coordination framework for highly sensitive and selective solid-phase microextraction of non-polar volatile organic compounds

A porous metal azolate framework [Zn(mpba)] (MAF-X8, H2mpba = 4-(3,5-dimethylpyrazol-4-yl)benzoic acid) with large, hydrophobic, one-dimensional channels and good thermal/chemical stability was synthesized and characterized. High-quality MAF-X8 thin films were grown on stainless-steel fibers for solid-phase microextraction (SPME), which showed high sensitivity and selectivity towards non-polar volatile organic compounds.

Chemical/Physical Pressure Tunable Spin-Transition Temperature and Hysteresis in a Two-Step Spin Crossover Porous Coordination Framework

A two-dimensional (2D) square-grid type porous coordination polymer [Fe(bdpt)(2)]·guest (1·g, Hbdpt = 3-(5-bromo-2-pyridyl)-5-(4-pyridyl)-1,2,4-triazole) with isolated small cavities was designed and constructed as a spin-crossover (SCO) material based on octahedral Fe(II)N(6) units and an all-nitrogen ligand. Three guest-inclusion forms were successfully prepared for 1·g (1·EtOH for g = ethanol, 1·MeOH for g = methanol, 1 for g = Null), in which the guest molecules interact with the framework as hydrogen-bonding donors. Magnetic susceptibility measurements showed that 1·g exhibited two-step SCO behavior with different transition temperatures (1·EtOH < 1·MeOH < 1) and hysteresis widths (1·EtOH > 1·MeOH > 1 ≈ 0). Such guest modulation of two-step spin crossover temperature and hysteresis without changing two-step state in a porous coordination framework is unprecedented. X-ray single-crystal structural analyses revealed that all two-step SCO processes were accompanied with interesting symmetry-breaking phase transitions from space group of P2(1)/n for all high-spin Fe(II), to P1 for ordered half high-spin and half low-spin Fe(II), and back to P2(1)/n for all low-spin Fe(II) again by lowering temperature. The different SCO behaviors of 1·g were elucidated by the steric mechanism and guest-host hydrogen-bonding interactions. The SCO behavior of 1·g can be also controlled by external physical pressure.

Synthesis and Adsorption Properties of Azulene-containing Porous Interdigitated Framework

Abstract A porous interdigitated 2D coordination framework {[Zn(azdc)(bpy)]·DMF}n (azdc: 1,6-azulenedicarboxylate; bpy: 4,4′-bipyridyl; DMF: N,N-dimethylformamide) was synthesized and structurally characterized. By comparing with its constitutional isomer, [Zn(azdc)(bpy)]n showed stronger H2O interaction which was induced by polarized azulene moiety.

Capture and separation of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; by porous coordination frameworks: Research progress and perspective

Porous coordination frameworks (PCF), which contain metal-organic and covalent-organic frameworks, are new types of porous materials constructed by coordination bonds between metal clusters/organic bridging ligands and organic building units. These materials have shown significant potential for CO₂ capture and separation due to their rich topology, high specific surface areas (SSAs), low densities, and tunable pore sizes. Here, we review the progress of capture and separation of CO₂ by PCF materials, and subsequently propose a scheme for the targeted design and synthesis of novel materials for CO₂ capture and separation <italic>via</italic> using a combination of experiment and the multiscale simulation. Finally, we also summarize several strategies for enhancing the CO₂ capture and separation ability of PCFs.

Super Flexibility of a 2D Cu-Based Porous Coordination Framework on Gas Adsorption in Comparison with a 3D Framework of Identical Composition: Framework Dimensionality-Dependent Gas Adsorptivities

Selective synthetic routes to coordination polymers [Cu(bpy)(2)(OTf)(2)](n) (bpy = 4,4'-bipyridine, OTf = trifluoromethanesulfonate) with 2- and 3-dimensionalities of the frameworks were established by properly choosing each different solvent-solution system. They show a quite similar local coordination environment around the Cu(II) centers, but these assemble in a different way leading to the 2D and 3D building-up structures. Although the two kinds of porous coordination polymers (PCPs) both have flexible frameworks, the 2D shows more marked flexibility than the 3D, giving rise to different flexibility-associated gas adsorption behaviors. All adsorption isotherms for N(2), CO(2), and Ar on the 3D PCP are of type I, whereas the 2D PCP has stepwise gas adsorption isotherms, also for CH(4) and water, in addition to these gases. The 3D structure, having hydrophilic and hydrophobic pores, shows the size-selective and quadrupole-surface electrical field interaction dependent adsorption. Remarkably, the 2D structure can accommodate greater amounts of gas molecules than that corresponding to the inherent crystallographic void volume through framework structural changes. In alcohol adsorption isotherms, however, the 2D PCP changes its framework structure through the guest accommodation, leading to no stepwise adsorption isotherms. The structural diversity of the 2D PCP stems from the breathing phenomenon and expansion/shrinkage modulation.

Structural Study of D2 within the Trimodal Pore System of a Metal Organic Framework

D2 loaded to saturation at 25 K into the porous coordination framework Cu3(1,3,5-benzenetricarboxylate)2 was studied using neutron powder diffraction. A saturation loading equivalent to 6.1 wt % H2 is reached at 25 K. D2 is located at up to nine distinct sites with six stable at saturation and three “metastable” sites at doses intermediate to saturation. Filling of the trimodal pore system is complex, and a concentration dependency on the optimal D2 arrangement is noted. A dynamic rearrangement of the D2 in the pores to a cubic-closed packed equilibrium structure occurs at doses close to saturation, with 4 D2 molecules arranged tetrahedrally in the smallest pore, 32 D2 arranged in a truncated octahedron with capped hexagonal faces in the intermediate sized pore, and 48 D2 arranged in a face-capped rhombic dodecahedron in the largest pore. The equilibrium structure of D2 in the largest pore at doses close to and at saturation was found to be the same arrangement that is optimal for 48 circles on a sphere. The structural response of the framework to D2 adsorption is dependent on the amount of D2, where the host lattice expands with increasing amount of adsorbed D2 at low and high D2 doses, and contracts upon adsorption of intermediate amounts of D2, commensurate with the known flexibility exhibited by this framework.

High heat of hydrogen adsorption and guest-responsive magnetic modulation in a 3D porous pillared-layer coordination framework

A bimetallic pillared-layer coordination framework {[Mn(3)(bipy)(3)(H(2)O)(4)][Cr(CN)(6)](2)·2(bipy)·4(H(2)O)}(n) has been constructed using a cyanometallate anion ([Cr(CN)(6)](3-)) and an organic linker (4,4'-bipyridyl) that provides high heat of hydrogen adsorption (∼11.5 kJ mol(-1)) and shows guest dependent magnetic modulation.

Assembly of Robust and Porous Hydrogen-Bonded Coordination Frameworks: Isomorphism, Polymorphism, and Selective Adsorption

By using the tripodal ligand ntb (tris(benzimidazole-2-ylmethyl)amine) and lanthanide nitrate, three isomorphous series of coordination frameworks of the general formula [Ln(ntb)(NO(3))(3)]·solvents (series 1: monoclinic C2/c, Ln = Gd(3+) and Yb(3+); series 2: hexagonal P3(1)/c, Ln = Nd(3+), Eu(3+), Gd(3+), and Er(3+); series 3, cubic Pa3̅, Ln = Gd(3+) and Er(3+); solvent = H(2)O or CH(3)OH) have been assembled and characterized with IR, elemental analyses, and single crystal and powder X-ray diffraction methods. In all isomorphous complexes, analogous [Ln(ntb)(NO(3))(3)] coordination monomers of the same structure act as the building blocks to be assembled via hydrogen bonds into three-dimensional (3D) frameworks. So the complexes of the same lanthanide ion (for example, the Gd(3+) ion) from three isomorphous series form polymorphs, for example, monoclinic polymorph 1-Gd, hexagonal polymorph 2-Gd, and cubic polymorph 3-Gd. The single-crystal analyses revealed that the polymorphism was related to different fashions of hydrogen bonding interactions, which was caused by different crystallization conditions, leading to the formation of different 3D hydrogen-bonded frameworks showing distinct porous and topological structures. The monoclinic and hexagonal crystals contain 1D channels, while the cubic crystal is nonporous. The thermogravimetric analyses indicated that all polymorphic crystals have high thermal stability against the removal of guest molecules, and the robust porosity of the hexagonal crystals has been verified by temperature-dependent single-crystal-to-single-crystal measurements upon guest removal/uptake. The solvents adsorption study disclosed that the porous frameworks show high selectivity of benzene against toluene and xylene, while the gas adsorption measurements indicated a moderate H(2), CO(2), and MeOH storage capacity in contrast to low N(2) uptake. The solid-state photoluminescence of the Eu(3+) and Nd(3+) complexes in the near-infrared and visible region has also been investigated, offering examples with optical properties tunable by means of isomorphous replacement.

Multiscale simulation and modelling of adsorptive processes for energy gas storage and carbon dioxide capture in porous coordination frameworks

Computational modelling is a powerful tool for the study of gas–solid interactions, and can be used both to complement experiment and design new materials. For the modelling of gas adsorption by nanoporous media, a multiscale approach can be used, in which the molecular force fields required for Grand Canonical Monte Carlo (GCMC) simulations are derived from first-principles calculations. This can result in significantly enhanced accuracy, in comparison with conventional empirical force field-based GCMC methods. In this article, we review the application of this multiscale approach to the simulation of the adsorption of hydrogen, methane and carbon dioxide in Porous Coordination Frameworks (PCFs) for the purpose of gas storage for energy transportation and Carbon Capture and Storage (CCS) technology. We also define a scheme for the design of new materials with improved adsorption performance for the storage of these gases through the combination of multiscale simulation and experimental work, and discuss some of the issues regarding gas adsorption measurement accuracy in the context of the validation of simulation results using experimental data.

Hydrogen Storage in Mesoporous Coordination Frameworks: Experiment and Molecular Simulation

A porous coordination framework material, Zn4O(BDC)(BTB)4/3 (labeled 1 for simplification), has been prepared and applied to hydrogen storage. Its storage capacity has been measured, and the absolute and excess H2 adsorption uptakes reach 6.23 and 5.43 wt % at 77 K and 20 bar, respectively. Moreover, a multiscale simulation method, which combines first-principles calculation and grand canonical Monte Carlo simulation, has been used to evaluate H2 adsorption in this material. The simulation results successfully reproduce the experimentally determined hydrogen uptake in 1 at T = 77 K and in the pressure range 0−20 bar. Furthermore, the simulation predicts that the hydrogen capacity in 1 reaches 9.5 wt % at 77 K and 100 bar, which is among the highest reported in the literature to date. Clearly, this material is a promising adsorbent for hydrogen storage.

Cover Picture: Heterogeneously Hybridized Porous Coordination Polymer Crystals: Fabrication of Heterometallic Core–Shell Single Crystals with an In‐Plane Rotational Epitaxial Relationship (Angew. Chem. Int. Ed. 10/2009)

AbstractA porous copper coordination framework grew epitaxially as a single crystal on the surface of a single crystal of a porous zinc coordination framework, as described by S. Kitagawa and co‐workers in their Communication on page 1766 ff. The picture shows the structural relationship between the copper and zinc frameworks, which has been unveiled by synchrotron surface X‐ray diffraction measurements; in‐plane rotational epitaxial growth compensates for the different lattice constants of the two crystals.magnified image