High CO2 Uptake Capacity and Selectivity in a Fascinating Nanotube-Based Metal–Organic Framework

Water Sorption Properties and Hydrothermal Stability of Al-Containing Metal-Organic Frameworks CAU-10 and MIL-96 Studied Using Quasi-Equilibrated Thermodesorption

A novel experimental technique, quasi-equilibrated temperature-programmed desorption and adsorption (QE-TPDA), was used to study the water sorption properties and hydrothermal stability of aluminum trimesate MIL-96 and aluminum isophthalate CAU-10, which have been selected due to their remarkable sorption properties. The QE-TPDA profiles of water observed for MIL-96 and CAU-10 confirmed the hydrophilic nature of these materials. Complex QE-TPDA profiles indicate that water sorption in MIL-96 follows a three-step pore filling mechanism. The shape of single desorption peaks in the QE-TPDA profiles for CAU-10 confirms that water sorption involves a reversible phase transition. Based on the QE-TPDA profiles, the water adsorption heat was determined: 45-46 kJ/mol for CAU-10 and 43-56 kJ/mol for MIL-96, in the latter case depending on the adsorption extent. Hydrothermal stability tests revealed that MIL-96 retained its stable porosity-related sorption capacity for water after hydrothermal treatment up to 290 °C. Gradual changes in the QE-TPDA profiles due to the hydrothermal treatment above 290 °C, with decreasing the high-temperature desorption peak and increasing the low-temperature one, indicate minor structural changes occurring in this material. Only after 410 °C treatment was fast degradation of MIL-96 observed. CAU-10 exhibited high and unchanged hydrothermal stability up to 400 °C.

Molecular engineering in a family of pillared-layered metal-organic frameworks for tuning gas adsorption behavior

In this work, inspired by a water-assisted three-dimensional supramolecular structure 1, we use a mixed-ligand strategy to form a 3D pillared-layered matrix by the introduction of linear ligands to compete against the water molecules. The resulting analogue microporous MOFs of 2-H, 2-F and 2-N, decorated with different functional groups, similarly show the CO2 uptake. Thanks to the negligible N2 adsorption capacity, enhanced selective adsorption towards CO2 is achieved in compound 2-N. That is, we present here an alternative plan for the high CO2 selective adsorption performance. In addition, the structure stability and moderate affinity for CO2 of these microporous MOFs endow them with excellent reusability.

Different Benzendicarboxylate-Directed Structural Variations and Properties of Four New Porous Cd(II)-Pyridyl-Triazole Coordination Polymers

Four new different porous crystalline Cd(II)-based coordination polymers (CPs), i. e., [Cd(mdpt)2]·2H2O (1), [Cd2(mdpt)2(m-bdc)(H2O)2] (2), [Cd(Hmdpt)(p-bdc)]·2H2O (3), and [Cd3(mdpt)2(bpdc)2]·2.5NMP (4), were obtained successfully by the assembly of Cd(II) ions and bitopic 3-(3-methyl-2-pyridyl)-5-(4-pyridyl)-1,2,4-triazole (Hmdpt) in the presence of various benzendicarboxylate ligands, i.e., 1,3/1,4-benzenedicarboxylic acid (m-H2bdc, p-H2bdc) and biphenyl-4,4'-bicarboxylate (H2bpdc). Herein, complex 1 is a porous 2-fold interpenetrated four-connected 3D NbO topological framework based on the mdpt- ligand; 2 reveals a two-dimensional (2D) hcb network. Interestingly, 3 presents a three-dimensional (3D) rare interpenetrated double-insertion supramolecular net via 2D ···ABAB··· layers and can be viewed as an fsh topological net, while complex 4 displays a 3D sqc117 framework. Then, the different gas sorption performances were carried out carefully for complexes 1 and 4, the results of which showed 4 has preferable sorption than that of 1 and can be the potential CO2 storage and separation material. Furthermore, the stability and luminescence of four complexes were performed carefully in the solid state.

Acid-Base-Resistant Metal-Organic Framework for Size-Selective Carbon Dioxide Capture

The development of practical porous materials for the selective capture of CO₂ from flue gas and crude biogas is highly critical for both environment protection and energy safety. Here, a novel metal-organic framework (FJI-H29) has been prepared, which not only has excellent acid-base resistance but also possesses polar micropores (3.4-4.3 Å) that can match CO₂ molecules well. FJI-H29 can selectively capture CO₂ from N₂ and CH₄ with excellent separation efficiency and suitable adsorption enthalpy under ambient conditions. Breakthrough experiments further confirm its practicability for both CO₂/N₂ and CO₂/CH₄ separation. All of these confirm FJI-H29 is a practical CO₂ adsorbent. Modeling calculations reveal that the confinement effect of micropores and the polar environment synergistically promotes the selective adsorption of CO₂, which will provide a potential strategy for the synthesis of a practical metal-organic framework for CO₂ capture.

Effecting structural diversity in a series of Co(II)-organic frameworks by the interplay between rigidity of a dicarboxylate and flexibility of bis(tridentate) spanning ligands

In a one-pot self-assembly reaction of Co(OAc)2·4H2O, thiophene-2,5-dicarboxylic acid (H2tdc) and four different bis(tridentate) polypyridyl spanning ligands under ambient conditions, a series of structurally diverse metal-organic frameworks has been synthesised and characterized by single crystal X-ray diffraction: {[Co2(tdc)2(tpbn)(H2O)2]·solvent}n (solvent = 2H2O, 1; solvent = 2CH3OH, 2H2O, 1a), {[Co2(tdc)2(tphn)]·solvent}n (solvent = H2O, 2; solvent = CH3OH, 2.5H2O, 2a), {[Co2(tdc)2(tpchn)(H2O)2]·solvent}n (solvent = 5H2O, 3; solvent = C2H5OH, 2H2O, 3a), and {[Co2(tdc)2(tpxn)]·solvent}n (solvent = 6H2O, 4; when no solvent, 4a), where tpbn (N,N',N'',N'''-tetrakis(2-pyridylmethyl)-1,4-diaminobutane), tphn = N,N',N'',N'''-tetrakis(2-pyridylmethyl)-1,6-diaminohexane, tpchn = N,N'-(cyclohexane-1,4-diylbis(methylene))bis(1-(pyridin-2-yl)-N-(pyridin-2-ylmethyl)methanamine) and tpxn = N,N'-(1,4-phenylenebis(methylene))bis(1-(pyridin-2-yl)-N-(pyridin-2-ylmethyl)methanamine). There is a profound effect of the nature of spacer between the alkyl nitrogens in the spanning ligands (flexible vs. semiflexible) on the molecular structures of 1a-4a. The notable differences are (a) the binding mode of the tridentate part of polypyridyl ligands to the Co(ii) center is facial in 1a, 3a and 4a but meridional in 2a, (b) the Co(ii) centers in 1a-3a are hexacoordinated (with a coordinated water in 1a and 3a) but are pentacoordinated in 4a, and (c) the binding mode of tdc linker is bis(monodentate) in 1a, 3a and 4a but chelated in one end and monodentate in the other end in 2a. Thus, the overall framework structure of 1a, 2a, 3a and 4a is cis-decalin type 2D polymer, ladder-shaped 1D polymer, hexagonal 2D net and cis-decalin type 2D polymer, respectively. Their thermal stabilities have been established by thermogravimetric analysis (TGA). The presence of an unsaturated metal center in 4 has provided us an opportunity for its use as an efficient Lewis acid catalyst for the Knoevenagel condensation reaction of malononitrile with various aldehydes (100% conversion in 60 minutes with 2 mol% catalyst in methanol).

Construction of a bifunctional Zn(ii)–organic framework containing a basic amine functionality for selective capture and room temperature fixation of CO2

The construction of a novel 3D, porous, bifunctional Zn(ii)–organic framework featuring two-types of 1D channels for efficient fixation of CO₂ to cyclic carbonates under solvent-free mild conditions of RT is reported.

Two novel lead-based coordination polymers for luminescence sensing of anions, cations and small organic molecules

A novel lead-based compound is reported as a multi-responsive luminescent sensor for detecting anions, cations and small organic molecules, especially Cr₂O₇²⁻, CrO₄²⁻, Fe³⁺ and nitrobenzene.

Facile Incorporation of Au Nanoparticles into an Unusual Twofold Entangled Zn(II)-MOF with Nanocages for Highly Efficient CO2 Fixation under Mild Conditions

Herein, a new porous Zn(II)-based metal-organic framework (MOF 1) has been prepared, the structure of which featured a twofold entangled motif based on two typical secondary building units (SBUs). The gas sorption studies indicated that MOF 1 may be explored as a useful platform to encapsulate metallic nanoparticles. Then the Au@1 composite has been prepared via a facile incorporation method without extra reducing agents. The Au@1 composite has been fully characterized by HRTEM, SEM-EDX, PXRD, gas sorption, XPS, ICP, etc. Catalytic experiments showed that the Au@1 composite had a perfect catalytic performance in CO₂ fixation for epoxides with different substituents under mild conditions.

Water-assisted proton conductivity of two highly stable imidazole multi-carboxylate-based MOFs

The proton conduction and proton mechanisms of two highly stable imidazole multi-carboxylate-based MOFs have been investigated and discussed.

Construction of a 3D porous Co(ii) metal–organic framework (MOF) with Lewis acidic metal sites exhibiting selective CO2 capture and conversion under mild conditions

The application of a 3D Co(ii)-MOF as a recyclable heterogeneous catalyst for conversion of CO₂ to cyclic carbonates is reported.

Doubly interpenetrated indium-tricarboxylate frameworks mediated by small molecules with enhanced porosity

A synthetic strategy of indium-tricarboxylate frameworks by using small molecule regulators has been proposed to obtain four types of In-based coordination polymers with doubly interpenetrated structures.

New multifunctional 3D porous metal–organic framework with selective gas adsorption, efficient chemical fixation of CO2 and dye adsorption

A new porous Mn(ii)-based MOF was obtained. The studies indicated it exhibits an effective storage capacity for CO₂, highly efficient catalyst behavior for epoxides with different substituents and rapid adsorption behavior of different dyes.

A robust and water-stable two-fold interpenetrated metal–organic framework containing both rigid tetrapodal carboxylate and rigid bifunctional nitrogen linkers exhibiting selective CO2 capture

A robust and water-stable two-fold interpenetrated metal–organic framework containing both rigid tetrapodal carboxylate and rigid bifunctional nitrogen linkers exhibiting selective CO₂ capture is reported.

Paddlewheel SBU based Zn MOFs: Syntheses, Structural Diversity, and CO₂ Adsorption Properties

Four Zn metal⁻organic frameworks (MOFs), {[Zn₂(2,6-ndc)₂(2-Pn)]·DMF}n (1), {[Zn₂(cca)₂(2-Pn)]·DMF}n (2), {[Zn₂(thdc)₂(2-Pn)]·3DMF}n (3), and {[Zn₂(1,4-ndc)₂(2-Pn)]·1.5DMF}n (4), were synthesized from zinc nitrate and N,N'-bis(pyridin-2-yl)benzene-1,4-diamine (2-Pn) with naphthalene-2,6-dicarboxylic acid (2,6-H₂ndc), 4-carboxycinnamic acid (H₂cca), 2,5-thiophenedicarboxylic acid (H₂thdc), and naphthalene-1,4-dicarboxylic acid (1,4-H₂ndc), respectively. MOFs 1⁻4 were all constructed from similar dinuclear paddlewheel {Zn₂(COO)₄} clusters and resulted in the formation of three kinds of uninodal 6-connected non-interpenetrated frameworks. MOFs 1 and 2 suit a topologic 4⁸·6⁷-net with 17.6% and 16.8% extra-framework voids, respectively, 3 adopts a pillared-layer open framework of 4⁸·6⁶·8-topology with sufficient free voids of 39.9%, and 4 features a pcu-type pillared-layer framework of 412·6³-topology with sufficient free voids of 30.9%. CO₂ sorption studies exhibited typical reversible type I isotherms with CO₂ uptakes of 55.1, 84.6, and 64.3 cm³ g-1 at 195 K and P/P₀ =1 for the activated materials 1', 2', and 4', respectively. The coverage-dependent isosteric heat of CO₂ adsorption (Qst) gave commonly decreased Qst traces with increasing CO₂ uptake for all the three materials and showed an adsorption enthalpy of 32.5 kJ mol-1 for 1', 38.3 kJ mol-1 for 2', and 23.5 kJ mol-1 for 4' at zero coverage.

An unprecedented water stable acylamide-functionalized metal–organic framework for highly efficient CH4/CO2 gas storage/separation and acid–base cooperative catalytic activity

HNUST-8 exhibits water stable, efficient CH₄/CO₂ storage and separation, acid–base cooperative catalytic activity in a tandem deacetalization Knoevenagel densation.

Lead-Based Metal-Organic Framework with Stable Lithium Anodic Performance

A microporous Pb-based metal-organic framework (MOF) [Pb(4,4'-ocppy)₂]·7H₂O (Pb-MOF) has been constructed from 4-(4-carboxyphenyl)pyridine N-oxide and Pb(NO₃)₂. Structural analysis reveals that the Pb-MOF possesses three-dimensional framework with a one-dimensional rhombic channel. When tested as a lithium-ion battery anode, a reversible lithium storage capacity of 489 mAh g^-1 was maintained after 500 cycles at 100 mA g^-1 as well as excellent cycling stability. The superior electrochemical performance may be derived from the sustenance of the Pb-MOF framework and compositional features of the organic moiety.

A new layer-stacked porous framework showing sorption selectivity for CO2 and luminescence

Luminescent Zn-MOF based stacked layers were assembled, featuring multiple CO₂-binding sites and selective CO₂ adsorption over CH₄.

Solvent-induced diversity of luminescent metal–organic frameworks based on different secondary building units

New complexes with SBUs were successfully assembled based on 5′-carboxyl-(1,1′-3′,1′′-terphenyl)-4,4′′-dicarboxylic acid and the CO₂ storage properties were researched.

A rare Pb9 cluster-organic framework constructed from a flexible cyclotriphosphazene-functionalized hexacarboxylate exhibiting selective gas separation

A rare Pb₉ cluster-based organic framework constructed from a flexible cyclotriphosphazene-functionalized hexacarboxylate exhibits selective adsorption separation of C₂ hydrocarbons and CO₂ from CH₄ under ambient conditions.

Acid–base directed supramolecular isomers of isophthalate based MOFs for CO2 adsorption and transformation

Directing supramolecular isomers using an acid versus a base, two MOFs with the same composition yet different topologies show differences in their catalytic efficacy to transform CO₂ and epoxides into cyclic carbonates.