Metal-Organic Framework Based on Pyrazinoquinoxaline Tetracarboxylic Acid for Fluorescence Sensing for Nitro Explosives

The rapid and selective detection of nitro explosives has become one of the current urgent environmental and safety issues. Fluorescent metal-organic frameworks (MOFs) provide strong support for the development of photoactive materials with excellent sensing performances. In this work, Zn2+ and pyrazinoquinoxaline tetracarboxylic acid with high nitrogen content were selected to construct a MOF structure termed Zn-MOF, which had excellent optical properties. The fluorescence sensing performance of Zn-MOF for nitro explosives was also investigated. The structural advantages of Zn-MOF, such as its porous structure, abundant host-guest interaction sites, and stable framework, ensure the prerequisites for various applications. Zn-MOF is not only capable of responding to a wide range of substrates, such as Fe3+, Cr2O72-, and MnO4-, to achieve fluorescence quenching detection but also able to achieve sensitive fluorescence sensing behavior for nitro explosives. In particular, for trinitrotoluene, the Ksv value can reach 8.72 × 103 M-1. The results show that the introduction of pyrazinoquinoxaline groups into MOFs can be an effective strategy for the preparation of highly efficient fluorescent sensing materials for nitro explosives.

Solvent-Free Coupling Reaction of Carbon Dioxide and Epoxides Catalyzed by Quaternary Ammonium Functionalized Schiff Base Metal Complexes under Mild Conditions

A series of bifunctional Schiff base metal catalysts (Zn-NPClR, Zn-NPXH, and M-NPClH) with two quaternary ammonium groups were prepared for carbon dioxide (CO₂) and epoxide coupling reactions. The effects of the reaction variables on the catalytic activity were systematically investigated, and the optimal reaction conditions (120 °C, 1 MPa CO₂, 3 h) were screened. The performances of different metal-centered catalysts were evaluated, and Co-NPClH showed excellent activity. This kind of bifunctional catalyst has a wide range of substrate applicability, excellent stability, and can be reused for more than five runs. A relatively high TOF could reach up to 1416 h^-1 with Zn-NPClH as catalyst by adjusting reaction factors. In addition, the kinetic study of the coupling reaction catalyzed by three catalysts (Zn, Co, and Ni) was carried out to obtain the activation energy (E_a) for the formation of cyclic carbonates. Finally, a possible mechanism for this cyclization reaction was proposed.

Luminescent metal–organic framework-based phosphor for the detection of toxic oxoanions in an aqueous medium

Compound 1 has been utilized for the luminescence based visible detection of chromate, permanganate and phosphate ions in aqueous medium.

Three new ZnII coordination polymers constructed from a semi-rigid tricarboxylic acid: structural changes caused by flexibility and luminescence sensing for hexavalent chromate anions

Coordination polymers (CPs) with specific structures and functional luminescence have been widely designed as sensors for detecting small molecules and ions. In this study, with or without the help of an N-donor auxiliary linker, three new Zn^II CPs, namely, three-dimensional (3D) poly[[pentaaquabis[μ₃-5-(4-carboxybenzyloxy)isophthalato]bis[μ₆-5-(4-carboxylatobenzyloxy)isophthalato]di-μ₃-hydroxido-hexazinc(II)] trihydrate], {[Zn₆(C₁₆H₁₀O₇)₂(C₁₆H₉O₇)₂(OH)₂(H₂O)₅]·3H₂O}_n or {[Zn₆(μ₃-HL)₂(μ₆-L)₂(μ₃-OH)₂(H₂O)₅]·3H₂O}_n, (I), one-dimensional (1D) catena-poly[[[aqua(1,10-phenanthroline)zinc(II)]-μ₂-5-(4-carboxybenzyloxy)isophthalato] dihydrate], {[Zn(C₁₆H₁₀O₇)(C₁₂H₈N₂)(H₂O)]·2H₂O}_n or {[Zn(μ₂-HL)(phen)(H₂O)]·2H₂O}_n (phen is 1,10-phenanthroline), (II), and 3D poly[diaquatetrakis(4,4'-bipyridine)bis[μ₆-5-(4-carboxylatobenzyloxy)isophthalato]di-μ₃-formato-di-μ₃-hydroxido-pentazinc(II)], [Zn₅(C₁₆H₉O₇)₂(HCOO)₂(OH)₂(C₁₀H₈N₂)₄(H₂O)₂]_n or [Zn₅(μ₄-L)₂(bpy)₄(μ₂-OH)₂(μ₃-HCOO)₂(H₂O)₂]_n (bpy is 4,4'-bipyridine), (III), have been constructed from the semi-rigid tricarboxylic acid 5-(4-carboxybenzyloxy)isophthalic acid (H₃L) under hydrothermal conditions. CP (I) exhibits a twofold interpenetrated 3D+3D→3D skeleton with a 3,5-conn topology constructed from triangular trinuclear [Zn₃(COO)₄(μ₃-OH)] clusters, in which the H₃L ligand adopts three different coordination modes. CP (II) exhibits a 1D infinite chain and stacking that gives a 3D structure mediated by hydrogen bonds and weak interactions. CP (III) is an interesting 3D 3,4,8-conn network including linear tetranuclear [Zn₄(μ₂-OH)₂(HCOO)₂(COO)₂] clusters with a new {4·6²}₂{4·6⁴·8}{4⁶·6¹⁹·8³} topological symbol. The influences of the flexible -CH₂-O- linker of the H₃L ligand and subtle environmental factors, such as solvent, pH value and auxiliary ligands, on the formation of the final structures are also discussed. The solid-state fluorescence spectra of CPs (I)-(III) were recorded at room temperature and all show better fluorescence performances than H₃L. In particular, (II) can act as a potential multifunctional fluorescent material for sensing hexavalent chromium ions in aqueous solution with high stability, selectivity and sensitivity. Under ultraviolet light of 365 nm from a UV lamp, a signal response of fluorescence from turning on to off can be observed with the naked eye. It was found that the detection for hexavalent chromium (i.e. Cr₂O₇^2-) by (II) has a high selectivity [K_SV = 1.61 × 10⁴ M^-1 and limit of detection (LOD) = 0.434 µM] in aqueous solution. Quenching mechanisms were also studied in detail.

A fluorescent probe for sequential sensing of MnO4− and Cr2O72− ions in aqueous medium based on a UCNS/TMB nanosystem

Distinguishable and sequential detection of MnO₄⁻ and Cr₂O₇²⁻ was realized by the reactions above and IFE between UCNS and oxTMB.

Two luminescent coordination polymers as highly selective and sensitive chemosensors for CrVI-anions in aqueous medium

Two luminescent coordination polymers with considerable stability in aqueous media were synthesized. Sensing experiments indicate that they can serve as highly selective and sensitive fluorescent probes toward Cr^VI-anions.

Construction of functional coordination polymers derived from designed flexible bis(4-carboxybenzyl)amine

A series of coordination polymers (CPs) have been constructed from bis(4-carboxybenzyl)amine and a series of bis(imidazole) linkers. Luminescence sensing measurements indicate that two zinc-based CPs both show highly selective and sensitive sensing for acetone and Cr₂O₇²⁻/CrO₄²⁻.

Two 2D multiresponsive luminescence coordination polymers for selective sensing of Fe3+, CrVI anions and TNP in aqueous medium

Zn(ii)/Cd(ii)-based 2D coordination polymers have been synthesized as luminescence sensors for the selective and reversible sensing of Fe³⁺, CrO₄²⁻, Cr₂O₇²⁻ and TNP in water.

Four new metal–organic frameworks based on diverse secondary building units: sensing and magnetic properties

Four new metal–organic frameworks based on diverse secondary building units were assembled and 1 showed high selectivity in the detection of CrO₄²⁻, Cr₂O₇²⁻, MnO₄⁻ and Fe³⁺.

Three Zn(ii)-based MOFs for luminescence sensing of Fe3+ and Cr2O72− ions

Three zinc metal–organic frameworks (MOFs) have been hydrothermally synthesized. We explored their applications in detecting ions, and the result shows that they all show highly selective sensing for Fe³⁺ and Cr₂O₇²⁻ ions.

Seven luminescent metal–organic frameworks constructed from 5-(triazol-1-yl)nicotinic acid: luminescent sensors for CrVI and MnO4− ions in an aqueous medium

Seven new luminescent metal–organic frameworks were assembled and complex 2 shows high selectivity and sensitivity for CrO₄²⁻, Cr₂O₇²⁻ and MnO₄⁻ ions with low detection limits.

Two luminescent lanthanide(iii) metal–organic frameworks as chemosensors for high-efficiency recognition of Cr(vi) anions in aqueous solution

Two 12-connected sqc15 lanthanide(iii) MOFs act as luminescent turn-off chemosensors for high-efficiency recognition of Cr₂O₇²⁻ and CrO₄²⁻ anions in aqueous solution.

A multifunctional MOF as a recyclable catalyst for the fixation of CO2 with aziridines or epoxides and as a luminescent probe of Cr(vi)

A multifunctional metal-organic framework (1) can serve as an efficient and recyclable catalysts for the conversion of CO₂ with aziridines or epoxides. Furthermore, the material can also act as a recyclable luminescent probe for Cr(vi) species among twenty anions.

From 2D → 3D interpenetration to packing: N coligand-driven structural assembly and tuning of luminescent sensing activities towards Fe3+ and Cr2O72− ions

Three complexes were hydrothermally synthesized and exhibited excellent selectivity towards Fe³⁺ and Cr₂O₇²⁻.

Extremely stable europium-organic framework for luminescent sensing of Cr2O72− and Fe3+ in aqueous systems

A novel Eu-MOF which is extremely stable in an aqueous system over a wide pH range is reported as a dual functional Cr₂O₇²⁻ and Fe³⁺ sensor in aqueous environments.

Solvent-dependent variations of both structure and catalytic performance in three manganese coordination polymers

Three new Mn-based MOFs have been prepared, and a 3D framework can act as an efficient and recycled catalyst in CO₂ cycloaddition with different epoxides.