Family Of MOFs Research Articles

Methyl red based metal–organic frameworks for the selective and tuneable sensing of ammonia gas

This work examines a family of UiO-based MOFs built from terephthalic acid and a methyl red linker. The orange-red MOFs show a colourimetric response, changing to dark red with acid vapour, and yellow with base (ammonia) vapour.

Engineering a Series of Isoreticular Pillared Layer Ultramicroporous MOFs for Gas and Vapor Uptake.

The accurate design and systematic engineering of MOFs is a large challenge due to the randomness of the synthesis process. Isoreticular chemistry provides a powerful approach for the regulation of pore environment in a more predictable and precise way to systematically control gas/vapor adsorption performances. Herein, utilizing an effective strategy of altering the "pillared" motifs of pillared layer structures, three isoreticular ultramicroporous MOFs were successfully constructed. Combined with the reported parent MOFs and two other recorded isoreticular MOFs modified with -NH2 and -CH3, gas and vapor uptake performances of this family of isoreticular pillared layer MOFs were systematically explored.

A Bismuth-Based Metal–Organic Framework for Visible-Light-Driven Photocatalytic Decolorization of Dyes and Oxidation of Phenylboronic Acids

In this work, a Bi-based metal-organic framework (MOF; Bi-MMTAA) with 2-mercapto-4-methyl-5-thiazoleacetic acid (MMTAA) as the organic ligand is synthesized. The crystal structure of Bi-MMTAA was determined by single-crystal X-ray diffraction. Theoretical calculations reveal that Bi-MMTAA is a p-type semiconductor, and electrons can delocalize through the π-conjugation when excited by a photon with an energy higher than the Bi-MMTAA band gap, which is beneficial to charge separation and transfer. The photoelectrical properties suggest that free electrons can be produced over Bi-MMTAA under light irradiation. The photocatalytic results suggest that Bi-MMTAA can decolorize rhodamine B (RhB) and oxidize phenylboronic acid to phenol under visible light (λ > 420 nm), with superoxide radicals being the main reactive oxygen species. Our results enrich the family of Bi-based MOFs and may inspire further exploration of Bi-based MOFs, including both synthesis and potential applications.

Hydrophobicity and dielectric properties across an isostructural family of MOFs: a duet or a duel?

An isoreticular family of metal-organic frameworks is post-synthetically subjected to polymer grafting. Surface hydrophobicity analysis, adsorption experiments, and impedance spectroscopy characterise the water molecules adsorbed, both on the surface and in the pores, while resolving how molecular mobility is impacted.

Tunable Band Gaps in MUV-10(M): A Family of Photoredox-Active MOFs with Earth-Abundant Open Metal Sites.

Titanium-based metal-organic frameworks (Ti-MOFs) have attracted intense research attention because they can store charges in the form of Ti3+ and they serve as photosensitizers to cocatalysts through heterogeneous photoredox reactions at the MOF-liquid interface. Both the charge storage and charge transfer depend on the redox potentials of the MOF and the molecular substrate, but the factors controlling these energetic aspects are not well understood. Additionally, photocatalysis involving Ti-MOFs relies on cocatalysts rather than the intrinsic Ti reactivity, in part because Ti-MOFs with open metal sites are rare. Here, we report that the class of Ti-MOFs known as MUV-10 can be synthetically modified to include a range of redox-inactive ions with flexible coordination environments that control the energies of the photoactive orbitals. Lewis acidic cations installed in the MOF cluster (Cd2+, Sr2+, and Ba2+) or introduced to the pores (H+, Li+, Na+, K+) tune the electronic structure and band gaps of the MOFs. Through the use of optical redox indicators, we report the first direct measurement of the Fermi levels (redox potentials) of photoexcited MOFs in situ. Taken together, these results explain the ability of Ti-MOFs to store charges and provide design principles for achieving heterogeneous photoredox chemistry with electrostatic control.

Remarkable Structural Diversity between Zr/Hf and Rare-Earth MOFs via Ligand Functionalization and the Discovery of Unique (4, 8)-c and (4, 12)-connected Frameworks.

Ligand modification in MOFs provides great opportunities not only for the development of functional materials with new or enhanced properties but also for the discovery of novel structures. We report here that a sulfone-functionalized tetrahedral carboxylate-based ligand is capable of directing the formation of new and fascinating MOFs when combined with Zr4+/Hf4+ and rare-earth metal cations (RE) with improved gas-sorption properties. In particular, the resulting M-flu-SO2 (M: Zr, Hf) materials display a new type of the augmented flu-a net, which is different as compared to the flu-a framework formed by the nonfunctionalized tetrahedral ligand. In terms of properties, a remarkable increase in the CO2 uptake is observed that reaches 76.6% and 61.6% at 273 and 298 K and 1 bar, respectively. When combined with REs, the sulfone-modified linker affords novel MOFs, RE-hpt-MOF-1 (RE: Y3+, Ho3+, Er3+), which displays a fascinating (4, 12)-coordinated hpt net, based on nonanuclear [RE9(μ3-Ο)2(μ3-ΟΗ)12(-COO)12] clusters that serve as hexagonal prismatic building blocks. In the absence of the sulfone groups, we discovered that the tetrahedral linker directs the formation of new RE-MOFs, RE-ken-MOF-1 (RE: Y3+, Ho3+, Er3+, Yb3+), that display an unprecedented (4, 8)-coordinated ken net based on nonanuclear RE9-clusters, to serve as bicapped trigonal prismatic building units. Successful activation of the representative member Y-ken-MOF-1 reveals a high BET surface area and total pore volume reaching 2621 m2 g-1 and 0.95 cm3 g-1, respectively. These values are the highest among all RE MOFs based on nonanuclear clusters and some of the highest in the entire RE family of MOFs. The present work uncovers a unique structural diversity existing between Zr/Hf and RE-based MOFs that demonstrates the crucial role of linker design. In addition, the discovery of the new RE-hpt-MOF-1 and RE-ken-MOF-1 families of MOFs highlights the great opportunities existing in RE-MOFs in terms of structural diversity that could lead to novel materials with new properties.

Thermodynamic Evidence of Structural Transformations in CO2-Loaded Metal-Organic Framework Zn(MeIm)2 from Heat Capacity Measurements.

Metal-organic frameworks are a class of porous compounds with potential applications in molecular sieving, gas sequestration, and catalysis. One family of MOFs, zeolitic imidizolate frameworks (ZIFs), is of particular interest for carbon dioxide sequestration. We have previously reported the heat capacity of the sodalite topology of the zinc 2-methylimidazolate framework (ZIF-8), and in this Article we present the first low-temperature heat capacity measurements of ZIF-8 with various amounts of sorbed CO2. Molar heat capacities from 1.8 to 300 K are presented for samples containing up to 0.99 mol of CO2 per mol of ZIF-8. Samples with at least 0.56 mol of CO2 per mol of ZIF-8 display a large, broad anomaly from 70 to 220 K with a shoulder on the low-temperature side, suggesting sorption-induced structural transitions. We attribute the broad anomaly partially to a gate-opening transition, with the remainder resulting from CO2 rearrangement and/or lattice expansion. The measurements also reveal a subtle anomaly from 0 to 70 K in all samples that does not exist in the sorbate-free material, which likely reflects new vibrational modes resulting from sorbate/ZIF-8 interactions. These results provide the first thermodynamic evidence of structural transitions induced by CO2 sorption in the ZIF-8 framework.

A stable mixed lanthanide metal-organic framework for highly sensitive thermometry.

A family of lanthanide-based MOFs (Ln-MOFs) with high thermal and chemical stability have been successfully synthesized by a solvothermal method. Owing to the intrinsic robustness of the framework and temperature-dependent luminescence behaviour of lanthanides, Eu3+/Tb3+-mixed MOFs ([(CH3)2NH2]Eu0.036Tb0.964BPTC) have also been successfully synthesized and targeted for developing excellent luminescent thermometers. The obtained mixed Ln-MOF exhibits ratiometric temperature sensing based on the distinguished characteristic emission of lanthanides with a wide temperature range from 77 K to 377 K. Particularly, the temperature sensor shows good linear responses from 220 K to 310 K with the maximum relative sensitivities (Sm) of 9.42% per K at 310 K. This value is comparable to those of the most excellent Ln-MOF thermometers reported. Besides, the temperature-dependent luminescent colours could also be systematically tuned from green, through yellow to red with increasing temperature, which can be clearly and directly observed even by the naked eye or a camera, thus also allowing colorimetric luminescence thermometry.

Synthesis, structures, and properties of a family of 3d-based MOFs constructed from mixed ligands

By the use of co-ligands tri(2-carboxyethyl)-isocyanurate) (H3tci) and 1H-3-(3-pyridyl)-5-(4-pyridyl)-1,2,4-triazole (3,4′-bpt), three coordination complexes, [Co3(tci)2(3,4′-bpt)2(H2O)4]·4H2O (1), [Cu3(tci)2(3,4′-bpt)2]·2H2O (2), and [Zn3(tci)2(3,4′-bpt)2(H2O)4]·4H2O (3), have been prepared by solvothermal methods and characterized by physicochemical and spectroscopic methods. Complexes 1 and 3 adopt a 3D (34) topology with the short Schlafli symbol of (6.82)4(62.82.102), both of them exhibiting threefold-interpenetrated networks. Complex 2 has a 2D 4-connected topology with the short Schlafli symbol of (44.62). Variable-temperature magnetic susceptibility measurements indicate that complexes 1 and 2 have antiferromagnetic interactions between the metal ions.

Three isoreticular MOFs derived from nitrogen-functionalized diisophthalate ligands: exploring the positional effect of nitrogen functional sites on the structural stabilities and selective C2H2/CH4 and CO2/CH4 adsorption properties

The positional effect of nitrogen functional sites on the structural stability and gas adsorption property was explored in a family of ssa-type MOFs.

Fine Tuning of MOF-505 Analogues To Reduce Low-Pressure Methane Uptake and Enhance Methane Working Capacity.

We present a crystal engineering strategy to fine tune the pore chemistry and CH4 -storage performance of a family of isomorphic MOFs based upon PCN-14. These MOFs exhibit similar pore size, pore surface, and surface area (around 3000 m2 g-1 ) and were prepared with the goal to enhance CH4 working capacity. [Cu2 (L2)(H2 O)2 ]n (NJU-Bai 41: NJU-Bai for Nanjing University Bai's group), [Cu2 (L3)(H2 O)2 ]n (NJU-Bai 42), and [Cu2 (L4)(DMF)2 ]n (NJU-Bai 43) were prepared and we observed that the CH4 volumetric working capacity and volumetric uptake values are influenced by subtle changes in structure and chemistry. In particular, the CH4 working capacity of NJU-Bai 43 reaches 198 cm3 (STP: 273.15 K, 1 atm) cm-3 at 298 K and 65 bar, which is amongst the highest reported for MOFs under these conditions and is much higher than the corresponding value for PCN-14 (157 cm3 (STP) cm-3 ).

Tuning the selectivity of light hydrocarbons in natural gas in a family of isoreticular MOFs

The kinetic adsorption selectivity of methane versus other light hydrocarbons, present in natural gas, is tuned in a rationally synthesized family of isoreticular MOFs.

Dynamic breathing effect in metal-organic frameworks: Reversible 2D-3D-2D-3D single-crystal to single-crystal transformation

The flexible organic linker nitrilotris(methyl phosphonic acid) (H6nmp) was used to isolate a new family of MOFs by the self-assembly with La3+ cations using a fast and simple microwave synthetic approach. Sulfuric acid was included in the reaction media with two major functions: (i) to slow down the deprotonation of the organic linker, thus favouring crystal growth over nucleation; (ii) to block coordination sites usually occupied by phosphonic acids groups, with the aim to design more porous materials. The 2D layered material obtained, [La2(H4nmp)2(H2O)3(SO4)]·8H2O (1), undergoes spontaneous single-crystal to single-crystal (SC-SC) transformations at ambient temperature, which were followed by single-crystal and powder X-ray diffraction studies. The highly disordered water molecules in the channels are gradually removed originating in a consecutive fashion [La2(H4nmp)2(H2O)3(SO4)]·6H2O (2), [La2(H4nmp)2(H2O)3(SO4)]·2H2O (3) and [La2(H4nmp)2(H2O)2(SO4)]·H2O (4). Materials are structurally very similar, being composed of “2D” layers formed by metallic centers in a zigzag conformation connected by the organic linker. While 1 and 3 are, in a topological perspective, identical (the sole difference being on the number of crystallization water molecules), being a 4-connected uninodal 2D networks with point symbol of {44.62}, 2 and 4 are in turn a 4,5-connected binodal (point symbol of {44.62}{44.64}) and 5-connected uninodal (point symbol of {46.64}) 3D networks, respectively. The main difference in these networks is the group that connects the “2D” layers: while in 2 the connection is achieved by the sulfate ion, in 4 the phosphonic acid residue is the main responsible by the formation of the 3D network, with the sulfate ion being coordinated to only one Ln3+ center. Because of the continuous transformation in ambient conditions of 1–3, the full characterization description by elemental analysis, FTIR spectroscopy, thermogravimetry and electron microscopy (SEM and EDS) is presented only for the final and stable structure, 4.

Engineering Homochiral Metal-Organic Frameworks by Spatially Separating 1D Chiral Metal-Peptide Ladders: Tuning the Pore Size for Enantioselective Adsorption.

The reaction of the chiral dipeptide glycyl-L(S)-glutamate with Co(II) ions produces chiral ladders that can be used as rigid 1D building units. Spatial separation of these building units with linkers of different lengths allows the engineering of homochiral porous MOFs with enhanced pore sizes, pore volumes, and surface areas. This strategy enables the synthesis of a family of isoreticular MOFs, in which the pore size dictates the enantioselective adsorption of chiral molecules (in terms of their size and enantiomeric excess).

Stepwise Ligand Exchange for the Preparation of a Family of Mesoporous MOFs

A stepwise ligand exchange strategy is utilized to prepare a series of isoreticular bio-MOF-100 analogues. Specifically, in situ ligand exchange with progressively longer dicarboxylate linkers is performed on single crystalline starting materials to synthesize products with progressively larger mesoporous cavities. The new members of this series of materials, bio-MOFs 101-103, each exhibit permanent mesoporosity and pore sizes ranging from ~2.1-2.9 nm and surface areas ranging from 2704 to 4410 m(2)/g. The pore volume for bio-MOF 101 is 2.83 cc/g. Bio-MOF-102 and 103 have pore volumes of 4.36 and 4.13 cc/g, respectively. Collectively, these data establish this unique family of MOFs as one of the most porous reported to date.

CAU-3: A new family of porous MOFs with a novel Al-based brick: [Al2(OCH3)4(O2C-X-CO2)] (X = aryl)

A new family of Al-based MOFs denoted as CAU-3 (CAU = Christian-Albrechts-Universität) was discovered in the solvothermal system Al(3+)/aryldicarboxylic acid/NaOH/methanol by applying high-throughput-methods. The three compounds reported in this article [Al(2)(OCH(3))(4)BDC], [Al(2)(OCH(3))(4)BDC-NH(2)] and[Al(2)(OCH(3))(4)NDC] (BDC = 1,4-benzenedicarboxylate; NDC = 2,6-naphtalenedicarboxylate) are all based on the same unprecedented inorganic building unit [Al(12)(OCH(3))(24)](12+), which is a dodecameric cyclic aluminium-methanolate-cluster. The material CAU-3-NDC was found to exhibit the highest surface area as well as the highest micropore volume of all Al-based MOFs reported until now.

Luminescent lanthanide metal–organic frameworks with a large SHG response

A family of new luminescent lanthanide MOFs have been synthesized and display a strong second-harmonic generation response, which is 6.0 times that of KDP and phase matchable. The LnMOFs also exhibit typical luminescence emissions with high quantum yields (up to 70.0% for Tb).

Extending the family of Zn-based MOFs: synthetic approaches to chiral framework structures and MOFs with large pores and channels

Tri- and pentanuclear, kinetically stable SBUs were exploited for the preparation of the novel MOFs [Zn(3)(BTEB)(2)(DMF)(2)] and (Me(2)NH(2))[Zn(5)(BTEB)(3)(μ(3)-OH)(2)(DMF)(2)]. The applied synthetic approach results in topologies that are stabilised by tritopic benzene-trisethynylbenzoic acid (BTEB) linkers giving rise to chiral frameworks with large pores or channels.

Synthesis and Stability of Tagged UiO-66 Zr-MOFs

The development in the field MOF materials is moving from the discovery of new structures toward applications of the most promising materials. In most cases, specialized applications require incorporation of functional chemical groups. This work is a systematic investigation of the effect that simple substituents attached to the aromatic linker have on the stability and property to the parent MOF. A family of isoreticular MOFs, based on the UiO-66 structure was obtained from the three different linker ligands H2N−H2BDC, O2N−H2BDC, and Br−H2BDC. The physicochemical and chemical investigation of these materials demonstrate that this class of MOFs retains high thermal and chemical stabilities, even with functional groups present at the linker units. The results demonstrate the possibility of incorporating active functional groups into the UiO-66 structure almost without losing its exceptionally high thermal and chemical stability. It has been established that the functional groups, at least in the amino func...

Ligand flexibility and framework rearrangement in a new family of porous metal–organic frameworks

Ligand flexibility permits framework rearrangement upon evacuation and gas uptake in a new family of porous MOFs.