Enhanced Gas Uptake in a Microporous Metal-Organic Framework via a Sorbate Induced-Fit Mechanism

Selective adsorption and separation of C2 hydrocarbons in a "flexible-robust" metal-organic framework based on a guest-dependent gate-opening effect

The selective adsorption/separation of C₂ hydrocarbons has been realized in a "flexible-robust" MOF, Zn₂(Atz)₂Ox. Owing to the distinctive guest-dependent multistep adsorption behaviors and suitable guest-framework interactions, this MOF shows outstanding separation performance for C₂H₂/C₂H₄ mixtures in a wide range of temperature confirmed by a column breakthrough experiment.

Zinc and Cadmium Complexes of Pyridinemethanol Carboxylates: Metal Carboxylate Zwitterions and Metal-Organic Frameworks

The heterofunctional lactone furo[3,4-b]pyridin-5(7H)-one (L₁ ) undergoes a coordination-induced ring-opening reaction with Zn(NO₃ )₂  ⋅ 6H₂ O to yield the zwitterionic [Zn(L₁ ')₂ (H₂ O)₂ ] (1, L₁ '=2-(hydroxymethyl)nicotinate) with an uncoordinated carboxylate. The same reaction with Cd(NO₃ )₂  ⋅ 4H₂ O provides a two-dimensional (2D) network of [Cd(L₁ ')₂ ]_n (3) with the carboxylates coordinated to cadmium(II) propagating the assembly. The corresponding reactions of Zn(NO₃ )₂  ⋅ 6H₂ O and Cd(NO₃ )₂  ⋅ 4H₂ O with 2-(hydroxymethyl)isonicotinic acid (HL₂ ) generated zwitterionic [Zn(L₂ )₂ (H₂ O)₂ ] (2) and a 2D network [Cd(L₂ )₂ ]_n ⋅nDMF (4, DMF=N,N'-dimethylformamide), respectively. Complexes 1-4 are weakly emissive, giving ligand-centered emissions at 409 nm (1), 412/436 nm (2), 404 nm (3), and 412/436 nm (4) in CHCl₃ solutions upon excitation at 330 nm. This work points to the potential of using 'hidden' functionalities widely found in small organic molecules and natural products for the construction of coordination complexes with new functionality and potential applications.

Determination of the dehydration pathway in a flexible metal-organic framework by dynamic in situ x-ray diffraction

Understanding guest exchange processes in metal-organic frameworks is an important step toward the rational design of functional materials with tailor-made properties. The dehydration of the flexible metal-organic framework [Co(AIP)(bpy)0.5(H2O)]•2H2O was studied by novel in situ dynamic x-ray diffraction techniques. The complex mechanism of dehydration, along with the as-yet unreported metastable structures, was determined. The structural information obtained by the application of these techniques helps to elucidate the important guest-host interactions involved in shaping the structural landscape of the framework lattice and to highlight the importance of utilizing this technique in the characterization of functional framework materials.

Enhanced and Heteromolecular Guest Encapsulation in Nonporous Crystals of a Perfluorinated Triketonato Dinuclear Copper Complex

The flexible host framework of a perfluorinated mononuclear copper complex, [Cu(L¹ )₂ ] (1, HL¹ =3-hydroxy-1,3-bis(pentafluorophenyl)-2-propen-1-one), with a CuO₄ core reversibly encapsulated several organic guest molecules through electrostatic interactions in its crystals. Hence, the corresponding dinuclear complex, [Cu₂ (L² )₂ ] (2, H₂ L² =1,5-dihydroxy-1,5-bis(pentafluorophenyl)-1,4-pentadien-3-one), was prepared to enhance guest recognition and the ability to separate molecular mixtures. Complex 2 comprises a Cu₂ O₆ core and four pentafluorophenyl groups. In crystal 2, cavities are formed on the axial sites of the metal core that are surrounded by pentafluorophenyl groups. The crystal of 2 encapsulates various guest molecules, that is, benzene (3), toluene (4), xylene (5), mesitylene (6), durene (7), and anisole (8). X-ray crystallographic and thermogravimetric (TG) studies show that three guest molecules are present in the crystal cavities. The number of guest molecules found in complex 2 was higher than that in complex 1, for example, (2)₃ ⋅(6)₁₀ >1⋅(6)₂ , (2)₂ ⋅(7)₇ >1⋅7, or 2⋅(8)₃ >1⋅(8)₂ . Naphthalene (9), was encapsulated in 2 to give 2⋅(9)₃ , but not in 1. In the crystal of complex 2, heteromolecular guest encapsulation was confirmed, designated as 2⋅(3)₂ ⋅9. TG analysis indicates that the thermal stability of the guest-included crystals of 2 is higher than that of 1.

From Discrete Complexes to Metal-Organic Layered Materials: Remarkable Hydrogen Bonding Frameworks

A series of metal-organic coordination complexes based on alkaline-earth metal centers [Mg(II), Ca(II), and Ba(II)] and the ligand 5-aminoisophthalate (aip2-) revealed notable structural diversity, both in the materials' dimensionality and in their hydrogen bonding networks: [Mg(H2O)6]∙[Mg2(Haip)(H2O)10]∙(Haip)∙3(aip)∙10(H2O) (1) and [Mg(aip)(phen)(H2O)2]∙(H2O) (2) were isolated as discrete complexes (0D); [Ca(aip)(H2O)2]∙(H2O) (3), [Ca(aip)(phen)(H2O)2]∙(phen)∙(H2O) (4), and [Ba2(aip)2(phen)2(H2O)7]∙2(phen)∙2(H2O) (5) revealed metal-organic chain (1D) structures, while the [Ba(aip)(H2O)] (6) showed a metal-organic layered (2D) arrangement. Furthermore, most of these metal-organic coordination materials revealed interesting thermal stability properties, being stable at temperatures up to 450 °C.

Two zinc metal-organic framework isomers based on pyrazine tetracarboxylic acid and dipyridinylbenzene for adsorption and separation of CO2 and light hydrocarbons

Two highly porous metal-organic framework isomers Zn₂(TCPP)(DPB) (1 and 2, H₄TCPP = 2,3,5,6-tetrakis(4-carboxyphenyl)pyrazine and DPB = 1,4-di(pyridin-4-yl)benzene) were successfully synthesized using different solvents and acid species to adjust the topologies of these two MOFs. Both of them were constructed by paddlewheel Zn₂(COO)₄, TCPP^4-, and DPB ligands. In compound 1, the Zn₂(COO)₄ paddlewheel units were fitted together by the TCPP^4- ligands to form two-dimensional layers, which were further connected by DPB ligands as pillars to construct a two-fold catenated 3D framework. In compound 2, the cross-linkage of Zn₂(COO)₄ paddlewheel units and TCPP^4- ligands resulted in a three-dimensional framework of Zn-TCPP, in which DPB ligands coordinated to two axial vertical dinuclear Zn₂(COO)₄. Both activated MOFs exhibited permanent porosity with high BET areas (1324 m² g^-1 for 1 and 1247 m² g^-1 for 2) and possessed narrow pore size distributions (0.93 nm for 1 and 1.02 nm for 2). Moreover, the adsorption behaviors of the two activated MOFs for CO₂ and light hydrocarbons (C1, C2, and C3) at low pressure were evaluated and favorable selectivity was proven for C₃H₈/C₃H₆ over CH₄. These two MOF materials reported in this study for selective CO₂ and light hydrocarbon capture have immense potential applications for environmental protection.

Grafting functional groups in metal–organic frameworks for U(vi) sorption from aqueous solutions

Recent highlights of the organic groups-functionalized MOFs for uranium extraction from aqueous solution are discussed.

Combining unsaturated metal sites and narrow pores within a Co(ii)-based MOF towards CO2 separation and transformation

Combining unsaturated metal sites and narrow pores within one framework, a unique Co^II-MOF have been prepared, which reveals excellent selective CO₂ uptake over N₂ and CH₄, and good performances in catalytic CO₂ conversion to cyclic carbonates.

Optimizing supramolecular interactions in metal–organic frameworks for C2 separation

C₂ separation is of great importance in the petrochemical industry. This perspective presents current status and future challenges in the design of MOF materials for C₂ separation.

Stimuli-responsive structural changes in metal–organic frameworks

This feature article mainly summarizes how the structure of MOFs changes under external stimuli.

Two anthracene chromophore based metal–organic frameworks for gas adsorption and promising nitro aromatic sensing

Two novel metal–organic frameworks (MOFs) have been synthesized under solvothermal conditions. Studies on luminescence sensing show 1 and 2 are highly selective and recyclable in the detection of nitroaromatic explosives, especially for TNP.