Diaqua­bis­(1H-imidazole-4-carboxyl­ato-κ2 N 3,O)zinc

In the title compound, [Zn(C4H3N2O2)2(H2O)2], the ZnII ion is situated on a twofold rotation axis and exhibits a distorted octa­hedral coordination configuration. The equatorial plane contains two cis-oriented bidentate 1H-imidazole-4-carboxyl­ate ligands and the axial positions are occupied by two coordinated water mol­ecules. In the crystal structure, inter­molecular O—H⋯O and N—H⋯O hydrogen bonds link the mol­ecules into a three-dimensional supra­molecular network. There are π–π inter­actions between the imidazole rings, with a centroid-to-centroid distance of 3.504 (3) Å

Reversible Interlayer Sliding and Conductivity Changes in Adaptive Tetrathiafulvalene-Based Covalent Organic Frameworks.

Ordered interlayer stacking is intrinsic in two-dimensional covalent organic frameworks (2D COFs) and has strong implications on COF's optoelectronic properties. Reversible interlayer sliding, corresponding to shearing of 2D layers along their basal plane, is an appealing dynamic control of both structures and properties, yet it remains unexplored in the 2D COF field. Herein, we demonstrate that the reversible interlayer sliding can be realized in an imine-linked tetrathiafulvalene (TTF)-based COF TTF-DMTA. The solvent treatment induces crystalline phase changes between the proposed staircase-like sql net structure and a slightly slipped eclipsed sql net structure. The solvation-induced crystallinity changes correlate well with reversible spectroscopic and electrical conductivity changes as demonstrated in oriented COF thin films. In contrast, no reversible switching is observed in a related TTF-TA COF, which differs from TTF-DMTA in terms of the absence of methoxy groups on the phenylene linkers. This work represents the first 2D COF example of which eclipsed and staircase-like aggregated states are interchangeably accessed via interlayer sliding, an uncharted structural feature that may enable applications such as chemiresistive sensors

trans-Diaqua­bis­(1H-imidazole-4-carboxyl­ato-κ2 N 3,O 4)nickel(II)

In the title complex, [Ni(C4H3N2O2)2(H2O)2], the NiII ion is located on an inversion center and shows a distorted octa­hedral geometry, defined by two N,O-bidentate 1H-imidazole-4-carboxyl­ate ligands in the equatorial plane and two water mol­ecules in the axial positions. Inter­molecular N—H⋯O hydrogen bonds link the complex mol­ecules into layers parallel to (10), which are further linked into a three-dimensional supra­molecular network through O—H⋯O hydrogen bonds

Three-Component Covalent Organic Framework Nanosheets for the Detection of MicroRNAs

The development of new techniques for the detection of microRNAs (miRNAs) is highly desirable. Herein, a new crystalline three-component covalent organic framework (COF) termed EB-TAPB-TFP COF was synthesized under solvothermal conditions utilizing 1,3,5-triformylphloroglucinol, 1,3,5-tris(4-aminophenyl)benzene and ethidium bromide as monomers. Interestingly, EB-TAPB-TFP COF can be self-exfoliated into two-dimensional nanosheets (NSs) in an aqueous medium. The obtained EB-TAPB-TFP NSs exhibited a remarkable fluorescence intensity enhancement in the presence of a DNA-miRNA heteroduplex when compared to the presence of single-stranded DNA and other phosphate-based small molecules, making it promising in the detection of miRNA without tagging any fluorescent marker. Moreover, the EB-TAPB-TFP NSs can also be used as sensing material for the detection of a DNA-miRNA heteroduplex using the quartz crystal microbalance technique, which is in good agreement with the fluorescence sensing result. The exploration of COF-based sensors in this work demonstrates a new pathway for the selective detection of miRNAs

Three-Component Covalent Organic Framework Nanosheets for the Detection of MicroRNAs

The development of new techniques for the detection of microRNAs (miRNAs) is highly desirable. Herein, a new crystalline three-component covalent organic framework (COF) termed EB-TAPB-TFP COF was synthesized under solvothermal conditions utilizing 1,3,5-triformylphloroglucinol, 1,3,5-tris(4-aminophenyl)benzene and ethidium bromide as monomers. Interestingly, EB-TAPB-TFP COF can be self-exfoliated into two-dimensional nanosheets (NSs) in an aqueous medium. The obtained EB-TAPB-TFP NSs exhibited a remarkable fluorescence intensity enhancement in the presence of a DNA-miRNA heteroduplex when compared to the presence of single-stranded DNA and other phosphate-based small molecules, making it promising in the detection of miRNA without tagging any fluorescent marker. Moreover, the EB-TAPB-TFP NSs can also be used as sensing material for the detection of a DNA-miRNA heteroduplex using the quartz crystal microbalance technique, which is in good agreement with the fluorescence sensing result. The exploration of COF-based sensors in this work demonstrates a new pathway for the selective detection of miRNAs

Covalent Organic Frameworks as the Coating Layer of Ceramic Separator for High-Efficiency Lithium–Sulfur Batteries

Covalent organic frameworks (COFs) have been proven to be an efficient host material for trapping sulfur in lithium–sulfur batteries. However, the potential application as the coating layer of the separator has not been well-addressed yet. Here, we synthesized an imine-based COF, DMTA-COF, which exhibited an AB-stacking mode and had a pore size of 0.56 nm. For the first time, we applied this nanoporous COF as the coating layer of the ceramic separator; the corresponding cell gave an initial discharge capacity up to 1415 mA h/g, and 1000 mA h/g remained after 100 cycles at 0.5 C. The performance is much better than that of the pristine ceramic separator and the super-P coated ceramic separator, demonstrating that the nanopores in the composite separator can effectively block the polysulfide across the separator, thus reducing the “shuttle” effect and the loss of active materials. This study provides a new design strategy for separators in lithium–sulfur batteries

Resistive Switching Memory Performance of Two-Dimensional Polyimide Covalent Organic Framework Films.

Two-dimensional polyimide covalent organic framework (2D PI-NT COF) films were constructed on indium tin oxide-coated glass substrates to fabricate two-terminal sandwiched resistive memory devices. The 2D PI-NT COF films condensated from the reaction between 4,4',4″-triaminotriphenylamine and naphthalene-1,4,5,8-tetracarboxylic dianhydride under solvothermal conditions demonstrated high crystallinity, good orientation preference, tunable thickness, and low surface roughness. The well-aligned electron-donor (triphenylamine unit) and -acceptor (naphthalene diimide unit) arrays rendered the 2D PI-NT COF films a promising candidate for electronic applications. The memory devices based on 2D PI-NT COF films exhibited a typical write-once-read-many-time resistive switching behavior under an operating voltage of +2.30 V on the positive scan and -2.64 V on the negative scan. A high ON/OFF current ratio (>106 for the positive scan and 104-106 for the negative scan) and long-term retention time indicated the high fidelity, low error, and high stability of the resistive memory devices. The memory behavior was attributed to an electric field-induced intramolecular charge transfer in an ordered donor-acceptor system, which provided the effective charge-transfer channels for injected charge carriers. This work represents the first example that explores the resistive memory properties of 2D PI-COF films, shedding light on the potential application of 2D COFs as information storage media