Highly Robust Microporous Metal-Organic Frameworks for Efficient Ethylene Purification under Dry and Humid Conditions

Two C₂ H₆ -selective metal-organic framework (MOF) adsorbents with ultrahigh stability, high surface areas, and suitable pore size have been designed and synthesized for one-step separation of ethane/ethylene (C₂ H₆ /C₂ H₄ ) under humid conditions to produce polymer-grade pure C₂ H₄ . Experimental results reveal that these two MOFs not only adsorb a high amount of C₂ H₆ but also display good C₂ H₆ /C₂ H₄ selectivity verified by fixed bed column breakthrough experiments. Most importantly, the good water stability and hydrophobic pore environments make these two MOFs capable of efficiently separating C₂ H₆ /C₂ H₄ under humid conditions, exhibiting the benchmark performance among all reported adsorbents for separation of C₂ H₆ /C₂ H₄ under humid conditions. Moreover, the affinity sites and their static adsorption energies were successfully revealed by single crystal data and computation studies. Adsorbents described in this work can be used to address major chemical industrial challenges.

A series of four novel alkaline earth metal-organic frameworks constructed of Ca(ii), Sr(ii), Ba(ii) ions and tetrahedral MTB linker: structural diversity, stability study and low/high-pressure gas adsorption properties

A series of four novel microporous alkaline earth metal–organic frameworks (AE-MOFs) containing methanetetrabenzoate linker (MTB) with composition {[Ca₄(μ₈-MTB)₂]·2DMF·4H₂O}_n (UPJS-6), {[Ca₄(μ₄-O)(μ₈-MTB)_3/2(H₂O)₄]·4DMF·4H₂O}_n (UPJS-7), {[Sr₃(μ₇-MTB)_3/2]·4DMF·7H₂O}_n (UPJS-8) and {[Ba₃(μ₇-MTB)_3/2(H₂O)₆]·2DMF·4H₂O}_n (UPJS-9) (UPJS = University of Pavol Jozef Safarik) have been successfully prepared and characterized. The framework stability and thermal robustness of prepared materials were investigated using thermogravimetric analysis (TGA) and high-energy powder X-ray diffraction (HE-PXRD). MOFs were tested as adsorbents for different gases at various pressures and temperatures. Nitrogen and argon adsorption showed that the activated samples have moderate BET surface areas: 103 m² g⁻¹ (N₂)/126 m² g⁻¹ (Ar) for UPJS-7′′, 320 m² g⁻¹ (N₂)/358 m² g⁻¹ (Ar) for UPJS-9′′ and UPJS-8′′ adsorbs only a limited amount of N₂ and Ar. It should be noted that all prepared compounds adsorb carbon dioxide with storage capacities ranging from 3.9 to 2.4 wt% at 20 °C and 1 atm, and 16.4–13.5 wt% at 30 °C and 20 bar. Methane adsorption isotherms show no adsorption at low pressures and with increasing pressure the storage capacity increases to 4.0–2.9 wt% of CH₄ at 30 °C and 20 bar. Compounds displayed the highest hydrogen uptake of 3.7–1.8 wt% at −196 °C and 800 Torr among MTB containing MOFs.

Four novel microporous alkaline earth metal–organic frameworks (AE-MOFs) containing methanetetrabenzoate linker (MTB): UPJS-6, UPJS-7, UPJS-8 and UPJS-9 have been successfully prepared, characterized and tested as adsorbents for different gases.

A cyano-bridged Cu(i)-based organic framework coupled with the C-C bond cleavage of acetonitrile for selective and sensitive sensing of Fe3+ ions

A cyano-bridged Cu(i) organic framework based on [Cu6(CN)6]n was synthesized, in which cyano anions were generated in situ from the C-C bond cleavage of acetonitrile. The as-synthesized compound displays orange-red luminescence and is further proven to be a promising Fe3+ luminescent sensor with high selectivity and sensitivity.

Pore Space Partition in Metal-Organic Frameworks

Metal-organic framework (MOF) materials have emerged as one of the favorite crystalline porous materials (CPM) because of their compositional and geometric tunability and many possible applications. In efforts to develop better MOFs for gas storage and separation, a number of strategies including creation of open metal sites and implantation of Lewis base sites have been used to tune host-guest interactions. In addition to these chemical factors, the geometric features such as pore size and shape, surface area, and pore volume also play important roles in sorption energetics and uptake capacity. For efficient capture of small gas molecules such as carbon dioxide under ambient conditions, large surface area or high pore volume are often not needed. Instead, maximizing host-guest interactions or the density of binding sites by encaging gas molecules in snug pockets of pore space can be a fruitful approach. To put this concept into practice, the pore space partition (PSP) concept has been proposed and has achieved a great experimental success. In this account, we will highlight many efforts to implement PSP in MOFs and impact of PSP on gas uptake performance. In the synthetic design of PSP, it is helpful to distinguish between factors that contribute to the framework formation and factors that serve the purpose of PSP. Because of the need for complementary structural roles, the synthesis of MOFs with PSP often involves multicomponent systems including mixed ligands, mixed inorganic nodes, or both. It is possible to accomplish both framework formation and PSP with a single type of polyfunctional ligands that use some functional groups (called framework-forming group) for framework formation and the remaining functional groups (called pore-partition group) for PSP. Alternatively, framework formation and PSP can be shouldered by different chemical species. For example, in a mixed-ligand system, one ligand (called framework-forming agent) can play the role of the framework formation while the other type of ligand (called pore-partition agent) can assume the role of PSP. PSP is sensitive to the types of inorganic secondary building units (SBUs). The coexistence of SBUs complementary in charge, connectivity, and so on can promote PSP. The use of heterometallic systems can promote the diversity of SBUs coexistent under a given condition. Heterometallic system with metal ions of different oxidation states also provides the charge tunability of SBUs and the overall framework, providing an additional level of control in self-assembly and ultimately in the materials' properties. Of particular interest is the PSP in MIL-88 type (acs-type topology) structure, which has led to a huge family of CPMs (called pacs CPMs, pacs = partitioned acs) exhibiting low isosteric heat of adsorption and yet superior CO₂ uptake capacity.

Lightweight Ionic Networks Composed of Li+ or Mg2+ Centres Linked Together by Dicarboxylate Ligands

The combination of lightweight metal cations with a range of dicarboxylate ligands has led to the generation of ionic network materials that possess channels occupied by solvent molecules. The compounds [Li₂ (2,2-bpdc)(DMF)₂ ] and [Mg(2,2-bpdc)(DMF)₂ ] (2,2-bpdc=2,2-dipyridyl-4,4-dicarboxylate) adopt a similar structure in which parallel metal-carboxylate chains are linked to four equivalent chains to generate a 3 D network in which DMF molecules occupy channels. [Li₄ (3,5-pdc)₂ (DMF)]⋅solvate (3,5-pdc=3,5-pyridine dicarboxylate) adopts a similar structure but the chains are more complex. As with the other structures, coordinated DMF molecules occupy network channels. [Li₄ (3,5-pdc)₂ (DMF)]⋅solvate is able to adsorb carbon dioxide at elevated pressures with the adsorption following a type V isotherm; hysteresis is apparent upon desorption. The final compound, Li[Mg₃ OH(2,2-bqdc)₃ (DMF/H₂ O)₃ ]⋅solvate (2,2-bqdc=2,2-biquinoline-4,4-dicarboxylate) has a distinctly different structure in which a trio of magnesium centres bound to a central μ₃ -hydroxide ion serves as a 6-connecting, trigonal prismatic node within a 3 D network that has the point symbol, 4⁹ 6⁶ . Solvent-filled intraframework spaces represent over 50 % of the crystal volume and are occupied by highly disordered solvent and Li⁺ ions. Immersion of Li[Mg₃ OH(2,2-bqdc)₃ (DMF/H₂ O)₃ ]⋅solvate in a solution of Fe(2,2-bipyridine)₃ ²⁺ results in the incorporation of the Fe^II complex into the large channels of the anionic network.

A Highly Water-Tolerant Magnesium(II) Coordination Polymer Derived from a Flexible Layered Structure

A two-dimensional (2D) layered Mg(II) coordination polymer (CP) with a high tolerance for H2 O was designed, synthesised, and crystallographically characterised. The synthesis was achieved by the introduction of a flexible 2D layered structure composed of Mg(II) ions and isonicotinate N-oxide ligands. Owing to its high H2 O tolerance, the obtained 2D layered structure has the flexibility to repeatedly adsorb a large amount of H2 O associated with interlayer expansion and enable the removal of H2 O from a H2 O/2-propanol mixed vapour. These results indicate that the CP could be an excellent dehydrating agent.

Framework Cationization by Preemptive Coordination of Open Metal Sites for Anion-Exchange Encapsulation of Nucleotides and Coenzymes

Cationic frameworks can selectively trap anions through ion exchange, and have applications in ion chromatography and drug delivery. However, cationic frameworks are much rarer than anionic or neutral ones. Herein, we propose a concept, preemptive coordination (PC), for targeting positively charged metal-organic frameworks (P-MOFs). PC refers to proactive blocking of metal coordination sites to preclude their occupation by neutralizing ligands such as OH(-) . We use 20 MOFs to show that this PC concept is an effective approach for developing P-MOFs whose high stability, porosity, and anion-exchange capability allow immobilization of anionic nucleotides and coenzymes, in addition to charge- and size-selective capture or separation of organic dyes. The CO2 and C2 H2 uptake capacity of 117.9 cm(3)  g(-1) and 148.5 cm(3)  g(-1) , respectively, at 273 K and 1 atm, is exceptionally high among cationic framework materials.

Synthesis, structure and adsorption properties of lanthanide-organic frameworks with pyridine-3,5-bis(phenyl-4-carboxylate)

Under solvothermal conditions, reactions of pyridine-3,5-bis(phenyl-4-carboxylic acid) (H2L) with lanthanide metal salts give rise to three new metal-organic frameworks (MOFs) with the formula {[Ln4(L)3(μ3-OH)4(H2O)4]·(NO3)2·solvent}n [Ln = Er (1), Yb (2) and Lu (3)]. The complexes were characterized by single crystal and powder X-ray diffraction, IR and thermogravimetric analyses. They have the same two-fold interpenetrating three-dimensional (3D) framework structures with [Ln4(COO)6(μ3-OH)4(H2O)4] clusters as secondary building units (SBUs) and a rare 6-connected lcy topology with the point (Schläfli) symbol of {3(3)·5(9)·6(3)}. Interestingly, 1-3 show selective and hysteretic sorption of CO2 over N2, and the photoluminescence properties of the complexes were also investigated.

Solvent-free synthesis of new magnesium phosphate–oxalates displaying diverse framework topologies

A series of open-framework magnesium phosphate–oxalates with pore apertures ranging from an 8-membered ring (8 MR) to 20 MR were prepared for the first time under solvent-free conditions.

A robust microporous metal–organic framework as a highly selective and sensitive, instantaneous and colorimetric sensor for Eu3+ ions

A highly thermostable Mg-MOF with nanoscale pores acts as a highly selective, sensitive and instantaneous sensor for Eu³⁺ in a water solution.

An infinite square lattice of super-supertetrahedral T(6)-like tin oxyselenide clusters

A new super-supertetrahedral cluster, resembling a coreless supertetrahedral T6 cluster, was made as a tin oxyselenide by integrating hard and soft Lewis bases (O(2-) and Se(2-)) into the tetravalent system. Its hierarchical architecture, built from supertetrahedral T3-[Sn10O4Se20] and Sn2Se6 clusters, represents a new level of complexity in the cluster-based construction. Compared to pure tin selenides, the new tin oxyselenide material in this work shows much enhanced stability and size-dependent band energy level.

Syntheses, structures, and properties of a series of 2D and 3D coordination polymers based on trifunctional pyridinedicarboxylate and different (bis)imidazole bridging ligands

Hydrothermal reactions based on two trifunctional pyridinedicarboxylate carboxylates and transitional metal cations in the presence of three (bis)imidazole bridging ligands afford ten 2D and 3D coordination polymers.

Self-assembly synthesis of precursors to potential open framework alkali earth metal–organic complexes

A series of magnesium pyridinecarboxylic–dicarboxylic acid complexes, synthesised as precursors to potential framework materials, show a range of metal ligand and hydrogen bonding geometries. The pyridinedicarboxylic complexes show most promise as precursors for further syntheses.

[M3(μ3-O)(O2CR)6] and related trigonal prisms: versatile molecular building blocks for crystal engineering of metal–organic material platforms

This review details the emergence of metal–organic materials (MOMs) sustained by high symmetry trigonal prismatic molecular building blocks (MBBs).