Coordination modulated on-off switching of flexibility in a metal-organic framework

Stimuli-responsive metal-organic frameworks (MOFs) exhibit dynamic, and typically reversible, structural changes upon exposure to external stimuli. This process often induces drastic changes in their adsorption properties. Herein, we present a stimuli-responsive MOF, 1·[CuCl], that shows temperature dependent switching from a rigid to flexible phase. This conversion is associated with a dramatic reversible change in the gas adsorption properties, from Type-I to S-shaped isotherms. The structural transition is facilitated by a novel mechanism that involves both a change in coordination number (3 to 2) and geometry (trigonal planar to linear) of the post-synthetically added Cu(i) ion. This process serves to 'unlock' the framework rigidity imposed by metal chelation of the bis-pyrazolyl groups and realises the intrinsic flexibility of the organic link.

Creative Construction of a Series of Chiral 3D Indium-Organic Frameworks with a umy Topology

Using 2,2'-R₂-biphenyl-4,4'-dicarboxylic acid to bind with a cis-[InO₄(μ₂-OH)₂] octahedron, three novel chiral 3D indium-organic frameworks, [In(μ₂-OH)L] [1, L¹, R = N(CH₃)₂; 2, L², R = OCH₃; 3, L³, R = CH₃], have been hydrothermally synthesized without chiral reagents. Crystal structure analyses reveal that 1-3 show an unprecedented 4-connected umy topology with the Schläfli symbol (4²·6⁴). 1 exhibits high water stability and good sorption selectivity of CO₂ over N₂, while 3 displays high C₂H₂, C₂H₄, and C₂H₆ uptake capacity at 273 K.

A review on production of metal organic frameworks (MOF) for CO2 adsorption

The environment sustenance and preservation of global climate are known as the crucial issues of the world today. Currently, the crisis of global warming due to CO₂ emission has turned into a paramount concern. To address such a concern, diverse CO₂ capture and sequestration techniques (CCS) have been introduced so far. In line with this, Metal Organic Frameworks (MOFs) have been considered as the newest and most promising material for CO₂ adsorption and separation. Due to their outstanding properties, this new class of porous materials a have exhibited a conspicuous potential for gas separation technologies especially for CO₂ storage and separation. Thus, the present review paper is aimed to discuss the adsorption properties of CO₂ on the MOFs based on the adsorption mechanisms and the design of the MOF structures. In addition, the main challenge associated with using this prominent porous material has been mentioned.

Unprecedented three-dimensional hydrogen-bonded hex topological chiral lanthanide–organic frameworks built from an achiral ligand

The design and preparation of chiral metal–organic frameworks (CMOFs) from achiral ligands are a big challenge. Using 3-nitro-4-(pyridin-4-yl)benzoic acid (HL) as a new linker, a total of eight chiral lanthanide–organic frameworks (LOFs), namely poly[diaquatris[μ2-3-nitro-4-(pyridin-4-yl)benzoato-κ2 O:O′]lanthanide(III)], L- and D-[Ln(C12H7N2O4)3(H2O)2] n [(1), Ln = Eu; (2), Ln = Gd; (3), Ln = Dy; (4), Ln = Tb], were hydrothermally synthesized without chiral reagents and determined by X-ray crystallography. Crystal structure analyses show that L-(1)–(4) crystallize in the hexagonal P65 space group and are isomorphous and isostructural, while the enantiomers D-(1)–(4) crystallize in the hexagonal P61 space group. All LnIII ions are octacoordinated by six carboxyl O atoms of six 3-nitro-4-(pyridin-4-yl)benzoate ligands and two water molecules in a dodecahedral geometry. A one-dimensional neutral helical [Ln2(CO2)3] n chain is observed in (1)–(4) as a chiral origin. These helical chains are further interconnected via directional hydrogen-bonding interactions between pyridyl groups and water molecules to construct a three-dimensional (3D) homochiral network with hex topology. The present CMOF structure is the first chiral 3D hydrogen-bonded hex-net and shows good water stability. Solid-state circular dichroism (CD) signals revealed that (1)–(4) crystallized through spontaneous resolution. Furthermore, (1) and (4) display a strong red and green photoluminescence at room temperature, respectively, but their intensities reduce to almost half at 200 °C. Notably, upon excitation under visible light (463 nm), a circularly polarized luminescence (CPL) of (1) in the solid state is observed for the first time, with a g lum value of 2.61 × 10−2.

Mixed-linker solid solutions of functionalized pillared-layer MOFs – adjusting structural flexibility, gas sorption, and thermal responsiveness

Structural flexibility in pillared-layer metal–organic frameworks can be controlled via the concept of mixed-linker solid solutions.

Solvent effects on the structures and magnetic properties of two doubly interpenetrated metal-organic frameworks

Two doubly interpenetrated coordination polymers [Co2(BDC)2(bpt)2]·nSolvent based on dimeric secondary building units and crystallizing with distinct solvent molecules (-H2O and -MeOH for nSolvent = 2H2O and MeOH·H2O, respectively) were obtained by employing 1,4-benzenedicarboxylate (BDC) and 1H-3,5-bis(4-pyridyl)-1,2,4-triazole) (bpt) as linkers. The structures consist of a square grid of dimers bridged by BDC and pillared by bpt. Thermogravimetry and PXRD indicate that the frameworks are stable and are retained up to 400 °C, but the structures are modified irreversibly. -H2O, high-symmetry Pna21, exhibits antiferromagnetic coupling within the dimer, while -MeOH, low-symmetry P21/n, exhibits ferromagnetic coupling. Upon desolvation, the -de and -de couplings are antiferromagnetic but reduced. Subsequent resolvation to -H2O and -MeOH resulted in a slight increase of the antiferromagnetic coupling without attaining the virgin states. The interesting difference of magnetic properties between -H2O and -MeOH, the solvated/desolvated phases, particularly at low temperature, indicates that there is a prominent solvent effect.

Supramolecular-jack-like guest in ultramicroporous crystal for exceptional thermal expansion behaviour

The dynamic behaviours of host frameworks and guest molecules have received much attention for their great relevance with smart materials, but little has been developed to control or understand the host-guest interplay. Here we show that the confined guest can utilize not only molecular static effects but also bulk dynamic properties to control the host dynamics. By virtue of the three-dimensional hinge-like framework and quasi-discrete ultramicropores, a flexible porous coordination polymer exhibits not only drastic guest-modulation effect of the thermal expansion magnitude (up to 422 × 10(-6) K(-1)) and even the anisotropy but also records positive/negative thermal expansion coefficients of +482/-218 × 10(-6) K(-1). Moreover, single-crystal X-ray diffraction analyses demonstrate that the jack-like motion of the guest supramolecular dimers, being analogous to the anisotropic thermal expansion of bulk van der Waals solids, is crucial for changing the flexibility mode and thermal expansion behaviour of the crystal.

Capturing snapshots of post-synthetic metallation chemistry in metal-organic frameworks

Post-synthetic metallation is employed strategically to imbue metal-organic frameworks (MOFs) with enhanced performance characteristics. However, obtaining precise structural information for metal-centred reactions that take place within the pores of these materials has remained an elusive goal, because of issues with high symmetry in certain MOFs, lower initial crystallinity for some chemically robust MOFs, and the reduction in crystallinity that can result from carrying out post-synthetic reactions on parent crystals. Here, we report a new three-dimensional MOF possessing pore cavities that are lined with vacant di-pyrazole groups poised for post-synthetic metallation. These metallations occur quantitatively without appreciable loss of crystallinity, thereby enabling examination of the products by single-crystal X-ray diffraction. To illustrate the potential of this platform to garner fundamental insight into metal-catalysed reactions in porous solids we use single-crystal X-ray diffraction studies to structurally elucidate the reaction products of consecutive oxidative addition and methyl migration steps that occur within the pores of the Rh-metallated MOF, 1·[Rh(CO)2][Rh(CO)2Cl2].

Multifunctional MOFs through CO2fixation: a metamagnetic kagome lattice with uniaxial zero thermal expansion and reversible guest sorption

The properties of atmospheric CO₂fixation, metamagnetism, reversible guest adsorption and zero thermal expansion have been combined in a single robust MOF, [Cu₃(bpac)₃(CO₃)₂](ClO₄)₂·H₂O (1·H₂O).