Introduction
Nitrile COFs linkers refer to organic monomers that contain cyano functional group (a functional group of carbon and nitrogen atoms connected by three bonds, the chemical formula is -CN) used in the construction of COFs. In addition to the aldehydes, amines, catechol and alcohols, cyano is one of the most commonly found the functional groups in COFs. This functional group can react through condensation reactions to synthesize COFs in which a small molecular byproduct is generated. And thus there are many nitrile COFs linkers so far, and they are frequently used in synthesis of nitrogen-rich COFs. The most significant example is the synthesis of covalent triazine frameworks (CTFs) which are first synthesized by using ionothermal method by Kuhn et al. in 2008 and exhibit higher surface area and porosity. In addition, nitrile organic linkers are also used to construct other types of COFs materials and the obtained COFs play a huge role in many fields. It can be said that nitrile organic linkers are already an indispensable synthetic monomer in the field of COFs.
Fig. 1. Structures of some typical nitrile organic linkers.
Applications
Nitrile organic linkers can be used in the synthesis of various COFs, and they mainly include the following types.
- Synthesis of triazine-linked COFs: Nitrile organic linkers are widely used for synthesis of triazine-linked COFs (or CTFs) in a variety of conditions. The details are as follows [1]: (1) The ionothermal polymerization of nitrile monomers through Lewis acid−base interactions can be used to synthesize CTFs. For example, Thomas’s group first synthesized CTF-1 by the ionothermal polymerization of p-benzenedicarbonitrile monomer at 400 °C with molten ZnCl2 as the catalyst and solvent. (2) The microwave-assisted Brønsted acid polymerization of aromatic nitrile monomers can be also used to synthesize CTFs. This method uses trifluoromethanesulfonic acid (TFMS) as a catalyst for the trimerization of aromatic nitrile monomers into CTFs at room temperature with a shortened reaction time. CTFs by this method later proved effective for photocatalytic water splitting. (3) Hard-template-assisted Brønsted acid vapor catalyzed polymerization of nitrile monomers can be also used to synthesize CTFs. In this process, solutions of nitrile monomers are mixed with uniformly packed SiO2 nanoparticles (300 nm in size) which are used as templates. After evaporation of the solvent, polymerization of nitrile is carried out in a TFMS vapor atmosphere to synthesize hollow and porous structures of CTFs.
Fig. 2. Scheme showing a systematic hard-template-assisted approach for the synthesis of hollow and porous of CTFs.
- Synthesis of olefinic linked COFs: By the Knoevenagel condensation of benzyl cyanides and aldehydes in the presence of a base catalyst can prepare the olefinic-linked fully π-conjugated COFs. The first example of this type of COF is prepared by the condensation of 1,4-phenylenediacetonitrile and tetrakis(4-formylphenyl)pyrene (TFPPy) in the mixture of mesitylene/ dioxane (1/5 v/v) at 110 °C for 3 days. Nowadays, a series of sp2c-COFs have been synthesized by this strategy. The most typical example is that an olefin-linked 2D conjugated COF, namely 2DPPV, was synthesized by the polycondensation reaction of 1,4-phenylene diacetonitrile (DCB) and 1,3,5-tris(4-formylphenyl)benzene (TFPB) containing catalyst of Cs2CO3 [2-3].
Fig. 3. Synthesis of 2DPPV.
- Synthesis of mixed triazine-imine linked COFs: Polycondensation of nitrile-containing linker with carboxylic group can be used to synthesize mixed triazine-imine linked COFs. However, the only example in this category is TRITER-1, which was synthesized via a one-pot polycondensation reaction between 4-aminobenzonitrile and terephthalic acid in the presence of triflic acid. This framework of TRITER-1 is N-rich, thermally stable, and possesses a high surface area and supermicropores (1.5 nm) and an excellent CO2 uptake capacity of 58.9 wt% at 273 K under 5 bar pressure [2].
Fig. 4. Proposed structure of TRITER-1.
Alfa Chemistry offers a series of nitrile COFs linkers, which have been widely used to construct triazine-linked COFs, olefinic linked COFs, mixed triazine-imine linked COFs, etc. You can click on our product list for a detailed view. At the same time, we also offer product customization according to customer's detailed requirements. If you are interested in our products or have any questions or needs, please feel free to contact us. We will be happy to provide you with support and services.
References:
- Liao L., et al. Advances in the Synthesis of Covalent Triazine Frameworks[J]. ACS omega, 2023, 8(5): 4527-4542.
- Bhambri H., et al. Nitrogen-rich covalent organic frameworks: a promising class of sensory materials[J]. Materials Advances, 2022, 3(1): 19-124.
- Geng K., et al. Covalent organic frameworks: design, synthesis, and functions[J]. Chemical Reviews, 2020, 120(16): 8814-8933.
