A 2D Coordination Network That Detects Nitro Explosives in Water, Catalyzes Baylis–Hillman Reactions, and Undergoes Unusual 2D→3D Single-Crystal to Single-Crystal Transformation

A Water-Stable 2-Fold Interpenetrating cds Net as a Bifunctional Fluorescence-Responsive Sensor for Selective Detection of Cr(III) and Cr(VI) Ions

Reactions of ZnSO₄∙7H₂O, N-(pyridin-3-ylmethyl)-4-(pyridin-4-yl)-1,8-naphthalimide (NI-mbpy-34), and 5-bromobenzene-1,3-dicarboxylic acid (Br-1,3-H₂bdc) afforded a luminescent coordination polymer, [Zn(Br-1,3-bdc)(NI-mbpy-34)]_n (1), under hydro(solvo)thermal conditions. Single-crystal X-ray structure analysis revealed that 1 features a three-dimensional (3-D) 2-fold interpenetrating cds (or CdSO₄) net topology with the point symbol of (6⁵·8), where the Zn(II) centers are considered as 4-connected square-planar nodes. X-ray powder diffraction (XRPD) patterns and thermogravimetric (TG) analysis confirmed that 1 shows high chemical and thermal stabilities. Notably, 1 displayed solvent dependent photoluminescence properties; the fluorescence intensity and emission maximum of 1 in different solvent suspensions varied when a solvent was changed. Furthermore, the H₂O suspension of 1 exhibited blue fluorescence emission and thus can be treated as a selective and sensitive fluorescent probe for turn-on detection of Cr³⁺ cations through absorbance caused enhancement (ACE) mechanism and turn-off detection of Cr₂O₇²⁻/CrO₄²⁻ anions through collaboration of the absorption competition and energy transfer process, with limit of detection (LOD) as low as μM scale.

Snapshots of Postsynthetic Modification in a Layered Metal-Organic Framework: Isometric Linker Exchange and Adaptive Linker Installation

Terminal ligand exchange and framework linker exchange have been frequently practiced as powerful tools to functionalize reticular structures such as metal-organic frameworks (MOFs). Herein, we report the postsynthetic modification (PSM) of a 6-connected layered MOF (hxl topology) to achieve a 12-connected fcu framework. In the PSM process, isometric linker exchange in the layers and linker installation between adjacent layers by the substitution of modulating ligands happen simultaneously. Snapshots of PSM at different time points reveal that the hxl domain is adaptively reorganized to create sites for new linker installation, and gradually the fcu domain dominates the crystal. Detailed kinetic analysis suggests that, although adaptive linker installation requires interlayer expansion of stackings in situ, it is kinetically faster than isometric linker exchange in the layers.

Engineered Bifunctional Luminescent Pillared-Layer Frameworks for Adsorption of CO2 and Sensitive Detection of Nitrobenzene in Aqueous Media

Through a dual-ligand synthetic approach, five isoreticular primitive cubic (pcu)-type pillared-layer metal-organic frameworks (MOFs), [Zn₂ (dicarboxylate)₂ (NI-bpy-44)]⋅x DMF⋅y H₂ O, in which dicarboxylate=1,4-bdc (1), Br-1,4-bdc (2), NH₂ -1,4-bdc (3), 2,6-ndc (4), and bpdc (5), have been engineered. MOFs 1-5 feature twofold degrees of interpenetration and have open pores of 27.0, 33.6, 36.8, 52.5, and 62.1 %, respectively. Nitrogen adsorption isotherms of activated MOFs 1'-5' at 77 K all displayed type I adsorption behavior, suggesting their microporous nature. Although 1' and 3'-5' exhibited type I adsorption isotherms of CO₂ at 195 K, MOF 2' showed a two-step gate-opening sorption isotherm of CO₂ . Furthermore, MOF 3' also had a significant influence of amine functions on CO₂ uptake at high temperature due to the CO₂ -framework interactions. MOFs 1-5 revealed solvent-dependent fluorescence properties; their strong blue-light emissions in aqueous suspensions were efficiently quenched by trace amounts of nitrobenzene (NB), with limits of detection of 4.54, 5.73, 1.88, 2.30, and 2.26 μm, respectively, and Stern-Volmer quenching constants (K_sv ) of 2.93×10³ , 1.79×10³ , 3.78×10³ , 4.04×10³ , and 3.21×10³  m^-1 , respectively. Of particular note, the NB-included framework, NB@3, provided direct evidence of the binding sites, which showed strong host-guest π-π and hydrogen-bonding interactions beneficial for donor-acceptor electron transfer and resulting in fluorescence quenching.

An exceptionally stable luminescent cadmium(ii) metal–organic framework as a dual-functional chemosensor for detecting Cr(vi) anions and nitro-containing antibiotics in aqueous media

Based on four kinds of SBUs, a robust Cd(ii) LMOF was fabricated that possessed highly sensitive detectability as a dual-response chemosensor for Cr(vi) anions and broad-spectrum nitro-containing antibiotics in aqueous media.

Amino group decorated coordination polymers for enhanced detection of folic acid

A series of fluorescent coordination polymers (CPs) {[Cd₂(CH₃-bpeb)₂(BDC)₂] CP1, (BDC)_0.5/(NH₂-BDC)_0.5-CP1, (BDC)_0.34/(NH₂-BDC)_0.66-CP1, (BDC)_0.25/(NH₂-BDC)_0.75-CP1, (BDC)_0.2/(NH₂-BDC)_0.8-CP1, (NH₂-BDC)-CP1} were prepared from conjugated ligand 4,4'-((2-methyl-1,4-phenylene)bis(ethene-2,1-diyl))bipyridine (CH₃-bpeb), terephthalic acid (BDC), aminoterephthalic acid (NH₂-BDC) and CdSO₄ under solvothermal conditions. The fluorescence of aqueous suspensions of these CPs was quenched by folic acid (FA) in a concentration dependent manner. The efficiency of quenching increasing with an increased proportion of NH₂-BDC ligand in the CP with (NH₂-BDC)-CP1 exhibiting a low detection limit of 1.7 × 10^-7 M.

Crystal structures and the ferroelectric properties of homochiral metal-organic frameworks constructed from a single chiral ligand

MOFs have proven to be promising candidates for designing ferroelectric materials. Herein, two new homochiral MOFs, Co-MOF-1 and Co-MOF-2, have been synthesized using the chiral ligand, HL (HL = phenyl-((pyridin-4-ylmethyl)-amino)-acetic acid), and Co(NO₃)₂·6H₂O. Co-MOF-1 was obtained via a two-step synthetic route involving a hydrogel to Zn-MOF conversion and a dissolution-recrystallization process. Co-MOF-2 was directly synthesized by a coordination reaction between chiral ligand, HL, and Co(NO₃)₂·6H₂O under hydrothermal conditions. We investigate the correlation between the ferroelectric properties of the samples and their crystal structures. The ferroelectric properties of Co-MOF-1 and Co-MOF-2 are drastically different. Indeed, Co-MOF-2 shows an obvious hysteretic behavior, while a clear electric hysteresis loop was not observed for Co-MOF-1. These significant disparities may be attributed to the different molecular dipole moments in Co-MOF-1 and Co-MOF-2. The different octahedral coordination units in the molecular structures of the Co-MOFs may alter the dipole moments of the molecules, resulting in the absence of a hysteresis loop for Co-MOF-1.

Interpol review of detection and characterization of explosives and explosives residues 2016-2019

This review paper covers the forensic-relevant literature for the analysis and detection of explosives and explosives residues from 2016-2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/Resources/Documents#Publications.

Zn(ii)/Cd(ii) based mixed ligand coordination polymers as fluorosensors for aqueous phase detection of hazardous pollutants

The recent developments and prospects of fluorosensors with a handful of recent examples based on mixed ligand Zn(ii)/Cd(ii) coordination polymers for aqueous phase detection of organic as well as inorganic pollutants have been discussed.

A quantitative transmetalation with a metal organic framework compound in a solid–liquid interface reaction: synthesis, structure, kinetics, spectroscopy and electrochemistry

A Zn(ii)-MOF (1) can be transformed to its isomorphous Cu(ii)-MOF (2) quantitatively in a single crystal to single crystal metal exchange process in a solid–liquid interface reaction.

Luminescence sensing, electrochemical, and magenetic properties of 2D coordination polymers based on the mixed ligands p-terphenyl-2,2′′,5′′,5′′′-tetracarboxylate acid and 1,10-phenanthroline

Four 2D CPs were constructed and provided platforms to investigate the electrochemical behavior, luminescence sensing of Cr(vi) and pesticides, and magnetic properties.

New linker installation in metal–organic frameworks

Installation of new organic components (including multitopic anionic and neutral linkers) in MOFs and MOPs for multicomponent materials.

Exploitation of the Flexidentate Nature of a Ligand To Synthesize Zn(II) Complexes of Diverse Nuclearity and Their Use in Solid-State Naked Eye Detection and Aqueous Phase Sensing of 2,4,6-Trinitrophenol

Three Zn(II) complexes, [Zn₂(HL)₂(NO₃)₂]·H₂O (1), [(Zn₄L₂)(μ₃-OH)₂](NO₃)₂·0.5H₂O (2), and [(Zn₆L₂)( o-van)₂(μ₃-OCH₃)₂(μ₃-OH)₂](NO₃)₂ (3), have been synthesized by exploiting the flexidentate nature of a multidentate Schiff base ligand, H₂L ( N, N'-bis(3-methoxysalicylidene)diethylenetriamine), by changing the reaction conditions and stoichiometry of the reactants. All three complexes are highly fluorescent in solution as well as in solid and have been used as luminescence sensors toward nitrophenol explosives in both the media. In aqueous/methanol medium, these complexes show very high selectivity and sensitivity with detection limit in ppb (2.03) or nM level (8.89 nM) for picric acid. The yellow color of all three Zn(II) complexes changes to red on mixing with small amount (∼5%) of picric acid in solid state, revealing the potential of these complexes for practical use in naked eye detection of 2,4,6-trinitrophenol (TNP) or picric acid in ambient light. In order to identify the host-guest interactions between Zn(II) complex and TNP, single crystals of the adduct of TNP with Zn(II) complex, [Zn₂(HL)₂(H₂O)₂][C₆H₂N₃O₇]₂ (4), were grown. Its X-ray crystal structure reveals that two picrate ions are attached to a dinuclear host with the help of H-bonding and π···π interactions, throwing light into the quenching mechanism and selectivity of detection.

Structural diversity, magnetic properties, and luminescence sensing of five 3D coordination polymers derived from designed 3,5-di(2′,4′-dicarboxylphenyl)benozoic acid

Five 3D CPs were constructed from a designed π-conjugated aromatic pentacarboxylate with diverse structures.

2D networks of metallo-capsules and other coordination polymers from a hexapodal ligand

2D M₃L₂ coordination polymers (M = Re(i), Cu(ii), Co(ii), Ni(ii)) feature metal-linked M₆L₂-cages, and the Re(i) material absorbs iodine.

Luminescent Zn(ii) coordination polymers as efficient fluorescent sensors for highly sensitive detection of explosive nitroaromatics

Zn CPs 1–3 exhibit strong blue/cyan fluorescence emissions in toluene suspension for highly selective and sensitive detection of explosive nitroaromatics through remarkable fluorescence quenching responses. In addition, the framework Zn²⁺ ions in 3 were partially substituted by Cu²⁺ ions via a single-crystal to single-crystal (SCSC) transformation.

A bifunctional cationic metal–organic framework based on unprecedented nonanuclear copper(ii) cluster for high dichromate and chromate trapping and highly efficient photocatalytic degradation of organic dyes under visible light irradiation

A bifunctional cationic MOF showed fast and highly efficient Cr₂O₇²⁻ and CrO₄²⁻ trapping, and highly efficient photocatalytic activity.