Post-modification of covalent organic framework functionalized aminated carbon nanotubes with active site (Fe) for the sensitive detection of luteolin.

In this research, the TT-COF(Fe)@NH2-CNTs was innovatively prepared through a post-modification synthetic process functionalized TT-COF@NH2-CNTs with active site (Fe), where TT-COF@NH2-CNTs was prepared via a one-pot strategy using 5,10,15,20-tetrakis (para-aminophenyl) porphyrin (TTAP), 2,3,6,7-tetra (4-formylphenyl) tetrathiafulvalene (TTF) and aminated carbon nanotubes (NH2-CNTs) as raw materials. The complex TT-COF(Fe)@NH2-CNTs material possessed porous structures, outstanding conductivity and rich catalytic sites. Thus, it can be adopted to construct electrochemical sensor with glassy carbon electrode (GCE). The TT-COF(Fe)@NH2-CNTs/GCE can selectively detect luteolin (Lu) with a wide linear plot ranging from 0.005 to 3 µM and a low limit of detection (LOD) of 1.45 nM (S/N = 3). The Lu residues in carrot samples were determined using TT-COF(Fe)@NH2-CNTs sensor and UV-visible (UV-Vis) approach. This TT-COF(Fe)@NH2-CNTs/GCE sensor paves the way for the quantification of Lu through a cost-efficient and sensitive electrochemical approach, which can make a significant step in the sensing field based on crystalline COFs.

Selective Construction and Structural Transformation of Homogeneous Linear Metalla[4]catenane and Metalla[2]catenane Assemblies.

Although the synthesis of mechanically interlocked molecules has been extensively researched, selectively constructing homogeneous linear [4]catenanes remains a formidable challenge. Here, we selectively constructed a homogeneous linear metalla[4]catenane in a one-step process through the coordination-driven self-assembly of a bidentate benzothiadiazole derivative ligand and a binuclear half-sandwich rhodium precursor. The formation of metalla[4]catenanes was facilitated by cooperative interactions between strong sandwich-type π-π stacking and non-classical hydrogen bonds between the components. Moreover, by modulating the aromatic substituents on the binuclear precursor, two homogeneous metalla[2]catenanes were obtained. The molecular structures of these metallacatenanes were unambiguously characterized by single-crystal X-ray diffraction analysis. Additionally, reversible structural transformation between metal-catenanes and the corresponding metallarectangles could be achieved by altering their concentration, as confirmed by mass spectrometry and NMR spectroscopy studies.

A Chiral Metal-Organic Framework Prepared on Large-Scale for Sensitive and Enantioselective Fluorescence Recognition.

MOF-based luminescent sensors have garnered considerable attention due to their potential in recognition and discrimination with high sensitivity, selectivity, and fast response in the last decades. Herein, this work describes the bulk preparation of a novel luminescent homochiral MOF, namely, [Cd(s-L)](NO3)2 (MOF-1), from an enantiopure pyridyl-functionalized ligand with rigid binaphthol skeleton under mild synthetic condition. Except for the features of porosity and crystallinity, the MOF-1 has also been characterized with water-stability, luminescence, and homochirality. Most important, the MOF-1 exhibits highly sensitive molecular recognition toward the4-nitrobenzoic acid (NBC) and moderate enantioselective detection of proline, arginine, and 1-phenylethanol.

Trefoil-Shaped Metal-Organic Cages as Fluorescent Chemosensors for Multiple Detection of Fe3+, Cr2O72-, and Antibiotics.

The construction of metal-organic cages (MOCs) with specific structures and fluorescence sensing properties is of much importance and challenging. Herein, a novel phenanthroline-based metal-organic cage, [Cd3L3·6MeOH·6H2O] (1), was synthesized by metal-directed assembly of the ligand 3,3'-[(1E,1'E)-(1,10-phenanthroline-2,9-diyl)bis(ethene-2,1-diyl)]dibenzoic acid (H2L) and CdI2 using a solvothermal method. According to single-crystal X-ray analysis, cage 1 exhibits a rare trefoil-shaped structure. Meanwhile, the discrete MOCs are further stacked into a 3D porous supramolecular structure through abundant intermolecular C-H···O interactions. Additionally, through exploration of fluorescence sensing on cations, anions, and antibiotics in aqueous solution, the experimental results indicate that cage 1 has excellent fluorescence sensing abilities for Fe3+, Cr2O72-, and nitrofuran and nitroimidazole antibiotics. The sensing ability of 1 remains unaltered for five cycles toward all analytes. The above results suggested that cage 1 can be considered a potential multiple sensor for the detection of Fe3+, Cr2O72-, and some antibiotics.

Template-Free Self-Assembly of Molecular Trefoil Knots and Double Trefoil Knots Featuring Cp*Rh Building Blocks.

Understanding and controlling the topology of self-assembled structures plays a fundamental role in supramolecular chemistry. Herein, the preparation of a series of tetranuclear metallarectangles and hexanuclear trefoil knots featuring Cp*Rh building blocks by template-free self-assembly with four different rigid and flexible ligands is described. Transformations between the trefoil knots and the corresponding macrocycles can be induced by using concentration effects. Remarkably, the hexanuclear trefoil knot 5 was shown to assemble further to provide rare examples of [12+1] heteronuclear double trefoil knots (5 a/5 b/5 c/5 d) through coordination of the amide oxygen atoms to the secondary metal ions Na+ /K+ /Ca2+ /Cd2+ . The synthetic results are supported by single-crystal XRD.

Coordination-driven self-assembly of a molecular figure-eight knot and other topologically complex architectures.

Over the past decades, molecular knots and links have captivated the chemical community due to their promising mimicry properties in molecular machines and biomolecules and are being realized with increasing frequency with small molecules. Herein, we describe how to utilize stacking interactions and hydrogen-bonding patterns to form trefoil knots, figure-eight knots and [2]catenanes. A transformation can occur between the unique trefoil knot and its isomeric boat-shaped tetranuclear macrocycle by the complementary concentration effect. Remarkably, the realization and authentication of the molecular figure-eight knot with four crossings fills the blank about 41 knot in knot tables. The [2]catenane topology is obtained because the selective naphthalenediimide (NDI)-based ligand, which can engender favorable aromatic donor-acceptor π interactions due to its planar, electron-deficient aromatic surface. The stacking interactions and hydrogen-bond interactions play important roles in these self-assembly processes. The advantages provide an avenue for the generation of structurally and topologically complex supramolecular architectures.

Highly Selective Synthesis of Iridium(III) Metalla[2]catenanes through Component Pre-Orientation by π⋠⋠⋠π†Stacking.

A series of molecular metalla[2]catenanes featuring Cp*Ir vertices have been prepared by the template-free, coordination-driven self-assembly of dinuclear iridium acceptors and 1,5-bis[2-(4-pyridyl)ethynyl]anthracene donors. The metalla[2]catenanes were formed by using a strategically selected linker type that is capable of participating in sandwich-type π-π stacking interactions. In the solid state, the [2]catenanes adopt two different configurations depending on the halogen atoms at the dinuclear metal complex bridge. Altering the solvent or the concentration, as well as the addition of guest molecules, enabled controlled transformations between metalla[2]catenanes and tetranuclear metallarectangles.

Light-initiated reversible conversion of macrocyclic endoperoxides derived from half-sandwich rhodium-based metallarectangles.

Although reversible photo-dimerization or oxygenation of anthracene and its derivatives is a common reaction, light-initiated reversible conversion of endoperoxide organometallic frameworks has only rarely been addressed. Herein, a series of tetranuclear organometallic macrocycles, [Cp*2Rh2(µ-C2O4-κO)]2(BP4VA)2(OTf)4 (4), [Cp*2Rh2(BiBzIm)]2(BP4VA)2(OTf)4 (5), and [Cp*2Rh2(DHBQ)]2(BP4VA)2(OTf)4 (6), were obtained in good yields from the reactions of the binuclear half-sandwich rhodium precursors [Cp*2Rh2(µ-C2O4-κO)Cl2] (1), [Cp*2Rh2(BiBzIm)Cl2] (2), and [Cp*2Rh2(DHBQ)Cl2] (3) with the 9,10-bis((E)-2-(pyrid-4-yl)vinyl)anthracene (BP4VA) ligand. The photochemical reaction of these metallarectangles was investigated by NMR and UV/vis spectroscopy. We have demonstrated that complexes 4, 5, and 6 can be reversibly and nearly quantitatively converted to the macrocyclic endoperoxides 4-O2, 5-O2, and 6-O2. Meanwhile, the structure of the endoperoxide photoproducts was unambiguously confirmed by 1H/13C NMR spectroscopy, IR spectroscopy, elemental analyses, and X-ray crystallography.

A nonanuclear triangular macrocycle and a linear heptanuclear heterometallic complex based on a 2-substituted imidazole-4,5-dicarboxylate ligand.

A Cp*Rh-based nonanuclear triangular macrocycle complex [(Cp*Rh)9L3(NO3)4.5(MeOH)](OTf)4.5 (1), a Cp*Ir-based trinuclear complex [(Cp*Ir)3L(MeCN)4](OTf)3 (2) and a linear heptanuclear heterometallic complex [(Cp*Ir)6ZnL2(MeCN)8(MeOH)2](OTf)8 (3) (Cp* = η(5)-pentamethylcyclopentadienyl) have been synthesized from a 2-(4-(pyridin-4-yl)phenyl)-1H-imidazole-4,5-dicarboxylic acid proligand. These complexes were further characterized by X-ray crystallography, (1)H NMR, DOSY NMR, IR spectroscopy, and elemental analyses.