Ligand Symmetry Modulation for Designing Mixed-Ligand Metal–Organic Frameworks: Gas Sorption and Luminescence Sensing Properties

Herein, we report the synthesis of a new mixed-linker Zn­(II)-based metal–organic framework (MOF), {[Zn₂(atz)₂­(bpydb)]­(DMA)₈}_<i>n</i> (<b>1</b>) (atz = deprotonated 3-amino-1,2,4-triazole, bpydb = deprotonated 4,4′-(4,4′-bipyridine-2,6-diyl) dibenzoic acid, DMA = <i>N</i>,<i>N</i>-dimethylacetamide), through symmetry modulation of a triazole ligand. The desymmetrized triazole linkers not only bond to the Zn­(II) ions to result in a new helical Zn-triazolate chain building unit but also lead to the formation of a highly porous framework (N₂ uptake: 617 cm³/g; BET surface area: 2393 m²/g) with 1D helical channels. The adsorption properties of desolved <b>1</b> were investigated by H₂, C₂H₂, CO₂, and CH₄ sorption experiments, which showed that <b>1</b> exhibited high uptake capacity for H₂ at 77 K and C₂H₂ around room temperature. More importantly, the high C₂H₂ uptake capacity but low binding energy makes this MOF a promising candidate for effective C₂H₂ capture from C₂H₂/CO₂ and C₂H₂/CH₄ mixed gases with low regenerative energy cost. In addition, <b>1</b> shows potential application for the luminescence sensing of small aromatic molecules picric acid (PA) and <i>p</i>-xylene (PX)

Stable Layered Semiconductive Cu(I)–Organic Framework for Efficient Visible-Light-Driven Cr(VI) Reduction and H₂ Evolution

Metal–organic frameworks (MOFs) have gained tremendous attention in the fields of environmental restoration and sustainable energy for their potential use as photocatalyst. Herein, a new two-dimensional (2D) Cu­(I)-based MOF material showing a narrow forbidden-band of 2.13 eV was successfully constructed using a visible-light-harvesting anthracene-based bipyridine ligand. The as-prepared MOF demonstrates high chemical stability and could be stable in the pH range 2–13, which is favorable for its potential application in photocatalysis. Photocatalytic experiments demonstrate that this Cu­(I)-MOF exhibits high reactivity for reduction of Cr­(VI) in water, with 95% Cr­(VI) converting to Cr­(III) in 10 min by using MeOH as scavenger under visible-light illumination. Furthermore, this MOF could behave as a highly active photocatalyst for H₂ evolution without additional photosensitizers and cocatalyst. Remarkably, the as-prepared MOF shows enhanced photocatalytic Cr­(VI) reduction and H₂ evolution performances compared with the pristine light-harvesting ligand under the same conditions. In connection to these, the photocatalytic reaction mechanism has also been probed

Dual-Emitting Dye@MOF Composite as a Self-Calibrating Sensor for 2,4,6-Trinitrophenol

An anionic metal–organic framework (MOF) {(NH₂Me₂)­[Zn₃(μ₃-OH)­(tpt)­(TZB)₃]­(DMF)₁₂}_<i>n</i> (<b>1</b>, tpt = 2,4,6-tri­(4-pyridyl)-1,3,5-triazine, H₂TZB = 4-(1<i>H</i>-tetrazol-5-yl)­benzoic acid and DMF = <i>N</i>,<i>N</i>-dimethylformamide), with both nanosized cages and partitions, has been solvothermally synthesized, which can serve as a crystalline vessel to encapsulate the fluorescent dye rhodamine 6G (Rh6G) via a “bottle around ship” approach. As a result, the obtained dye@MOF composite system features a blue emission of the ligand at 373 nm and a red emission of Rh6G at 570 nm when dispersed in solution, which could be used for decoding the trace amount of 2,4,6-trinitrophenol (TNP) by referring the peak-height ratio of each emission, even in coexistence with other potentially competitive nitroaromatic analytes. Furthermore, the observed fluorescence responses of the composite toward TNP are highly stable and reversible after recycling experiments. To the best of our knowledge, this is the first example of an MOF-implicated self-calibrated sensor for TNP detection

Two Isostructural Coordination Polymers Showing Diverse Magnetic Behaviors: Weak Coupling (Ni^II) and an Ordered Array of Single-Chain Magnets (Co^II)

Two isomorphic 3-D complexes with the formulas [M₃(TPTA) (OH)₂(H₂O)₄]_<i>n</i> (M = Ni for <b>1</b> and Co for <b>2</b>; H₄TPTA = [1,1′:4′,1″-terphenyl]-2′,3,3″,5′-tetracarboxylic acid) have been synthesized and magnetically characterized. Complexes <b>1</b> (Ni^II) and <b>2</b> (Co^II) have the same 1-D rod-shaped inorganic SBUs but exhibit significantly different magnetic properties. Complex <b>2</b>(Co^II) is a 3-D arrangement of a 1-D Co^II single-chain magnet (SCM), while complex <b>1</b>(Ni^II) exhibits weak coupling

Moisture-Stable Zn(II) Metal–Organic Framework as a Multifunctional Platform for Highly Efficient CO₂ Capture and Nitro Pollutant Vapor Detection

A moisture-stable three-dimensional (3D) metal–organic framework (MOF), {(Me₂NH₂)­[Zn₂(bpydb)₂(ATZ)]­(DMA)­(NMF)₂}_<i>n</i> (<b>1</b>, where bpydb = 4,4′-(4,4′-bipyridine-2,6-diyl)­dibenzoate, ATZ = deprotonated 5-aminotetrazole, DMA = <i>N</i>,<i>N</i>-dimethylacetamide, and NMF = <i>N</i>-methylformamide), with uncoordinated <i>N</i>-donor sites and charged framework skeleton was fabricated. This MOF exhibits interesting structural dynamic upon CO₂ sorption at 195 K and high CO₂/N₂ (127) and CO₂/CH₄ (131) sorption selectivity at 298 K and 1 bar. Particularly, its CO₂/CH₄ selectivity is among the highest MOFs for selective CO₂ separation. The results of Grand Canonical Monte Carlo (GCMC) simulation indicate that the polar framework contributes to the strong framework–CO₂ binding at zero loading, and the tetrazole pillar contributes to the high CO₂ uptake capacity at high loading. Furthermore, the solvent-responsive luminescent properties of <b>1</b> indicate that it could be utilized as a fluorescent sensor to detect trace amounts of nitrobenzene in both solvent and vapor systems

Tunable Robust pacs-MOFs: a Platform for Systematic Enhancement of the C₂H₂ Uptake and C₂H₂/C₂H₄ Separation Performance

As a modulatable class of porous crystalline materials, metal–organic frameworks (MOFs) have gained intensive research attention in the domain of gas storage and separation. In this study, we report on the synthesis and gas adsorption properties of two robust MOFs with the general formula [Co₃(μ₃-OH)­(cpt)₃Co₃(μ₃-OH)­(L)₃(H₂O)₉]­(NO₃)₄(guests)_<i>n</i> [L = 3-amino-1,2,4-triazole (<b>1</b>) and 3,5-diamino-1,2,4-triazole (<b>2</b>); Hcpt = 4-(4-carboxyphenyl)-1,2,4-triazole], which show the same pacs topology. Both MOFs are isostructural to each other and show MIL-88-type frameworks whose pore spaces are partitioned by different functionlized trinuclear 1,2,4-triazolate-based clusters. The similar framework components with different amounts of functional groups make them an ideal platform to permit a systematic gas sorption/separation study to evaluate the effects of distinctive parameters on the C₂H₂ uptake and separation performance. Because of the presence of additional amido groups, the MOF <b>2</b> equipped with a datz-based cluster (Hdatz = 3,5-diamino-1,2,4-triazole) shows a much improved C₂H₂ uptake capacity and separation performance over that of the MOF <b>1</b> equipped with atz-based clusters (Hatz = 3-amino-1,2,4-triazole), although the surface area of the MOF <b>1</b> is almost twice than that of the MOF <b>2</b>. Moreover, the high density of open metal sites, abundant free amido groups, and charged framework give the MOF <b>2</b> an excellent C₂H₂ separation performance, with ideal adsorbed solution theory selectivity values reaching up to 11.5 and 13 for C₂H₂/C₂H₄ (1:99) and C₂H₂/CO₂ (50:50) at 298 K and 1 bar, showing potential for use in natural gas purification

Quest for the <b>Ncb</b>-type Metal–Organic Framework Platform: A Bifunctional Ligand Approach Meets Net Topology Needs

A custom-designed bifunctional ligand was used to connect an <i>in situ</i> formed Co₃(OH) cluster affording a porous metal–organic framework, which represents the first case of <b>ncb</b>-type networks constructed from a single kind of ditopic ligand. Noticeably, the activated MOF shows high volumetric C₂H₂ uptake and excellent adsorption selectivity for C₂H₂/CO₂ separation at room temperature with a low sorption heat

Microporous Cobalt(II)–Organic Framework with Open O‑Donor Sites for Effective C₂H₂ Storage and C₂H₂/CO₂ Separation at Room Temperature

The self-assembly of a bifunctional organic ligand with a formate-bridged rod-shaped secondary building unit leads to a new microporous metal–organic framework (MOF). This MOF shows a moderately high C₂H₂ storage capacity (145 cm³/g) and an excellent adsorption selectivity for C₂H₂/CO₂ (11) at room temperature. Furthermore, its discriminatory sorption behavior toward C₂H₂ and CO₂ was probed by computational analysis in detail

Tracking the Superefficient Anion Exchange of a Dynamic Porous Material Constructed by Ag(I) Nitrate and Tripyridyltriazole via Multistep Single-Crystal to Single-Crystal Transformations

To avoid the instability and inefficiency for anion-exchange resins and layered double-hydroxides materials, we present herein a flexible coordination network [Ag­(L²⁴³)]­(NO₃)­(H₂O)­(CH₃CN) (L²⁴³ = 3-(2-pyridyl)-4-(4-pyridyl)-5-(3-pyridyl)-1,2,4-triazole) with superefficient trapping capacity for permanganate, as a group-7 oxoanion model for radiotoxic pertechnetate pollutant. Furthermore, a high-throughput screening strategy has been developed based on concentration-gradient design principle to ascertain the process and mechanism for anion exchange. Significantly, a series of intermediates can be successfully isolated as the qualified crystals for single-crystal X-ray diffraction. The result evidently indicates that such a dynamic material will show remarkable breathing effect of the three-dimensional host framework upon anion exchange, which mostly facilitates the anion trapping process. This established methodology will provide a general strategy to discover the internal secrets of complicated solid-state reactions in crystals at the molecular level

Lanthanide–Organic Coordination Frameworks Showing New 5‑Connected Network Topology and 3D Ordered Array of Single-Molecular Magnet Behavior in the Dy Case

Five isostructural lanthanide–organic coordination frameworks with a unique 3-D 5-connected (4⁷.6³)­(4³.6⁵.​8²) network, namely, [Ln­(phen)­(<b>L</b>)]_<i>n</i> (Ln = Dy for <b>1</b>, Gd for <b>2</b>, Ho for <b>3</b>, Er for <b>4</b>, and Tb for <b>5</b>), have been prepared based on bridging 5-hydroxyisophthalic acid (H₃<b>L</b>) and chelating 1,10-phenanthroline (phen) coligand. Significantly, the Dy­(III) complex <b>1</b> is an organized array of single-molecular magnets (SMMs), with frequency-dependent out-of-phase ac susceptibility signals and magnetization hysteresis at 4 K. Further analysis of the magnetic results can reveal that the SMM behavior of <b>1</b> should arise from the smaller ferromagnetic interaction between the Dy­(III) ions. Complex <b>1</b> was also characterized by X-ray absorption spectra, which give the clear X-ray magnetic circular dichroism signal