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New 3D COF structure could help tune porous materials for batteries and cleanup
A research team synthesized and determined the structure of a borate-linked 3D crystalline covalent organic framework, TCTP-COF, via electron diffraction for the first time. These findings will help scientists determine the structure-property relationships for other 3D COFs and facilitate their tuning for advanced applications.
Overcoming many of society's biggest challenges requires innovations in materials chemistry to achieve specific goals: carbon sequestration to mitigate climate change, absorbing toxic chemicals for environmental remediation and delivering life-saving compounds to cure disease, for example.
One type of compound, called three-dimensional covalent organic frameworks (3D COFs), shows promise in all of these potential applications. As a class of synthetic, highly ordered, porous crystalline polymers, specific 3D COFs can also be used as battery electrodes and as catalysts to speed chemical reactions, making them the subject of intense research and development.
Synthesizing highly ordered 3D COFs in a reliable manner remains challenging. To date, methods used to produce COFs often result in amorphous or poorly crystalline solids. This occurs because strong, directional covalent bonds form too rapidly, forcing the material into a disordered network instead of an ordered, thermodynamically stable crystal lattice. Because of this, atomic-level structures have been achieved for only a limited number of 3D COFs, hindering researchers' understanding of each 3D COF structure and its properties.
Borate linkages offer a new route
To address this issue, a group of researchers from the National Institute of Natural Sciences (NINS), Osaka University, Nagoya University, SOKENDAI and the Comprehensive Research Organization for Science and Society in Japan synthesized and determined the structure of a spiroborate-linked 3D crystalline COF using microcrystal electron diffraction (microED) methods for the first time, providing a new design strategy for expanding the synthesis and implementation of highly ordered 3D COF architectures.
The team published their article in the journal Science Advances.
"In this study, we focused on borate anions as a new linkage motif for constructing 3D crystalline COFs. Borates are known to form tetracoordinate spiro-type structures that are rigid and stable," said Yasutomo Segawa, associate professor in the Institute for Molecular Science and The Graduate University for Advanced Studies, SOKENDAI in Okazaki, Japan, and senior author of the research paper.
"A previous report of crystalline one-dimensional polymers featuring borate-based linkages further suggests that this motif could be extended to the construction of highly crystalline 3D COFs. Although several 3D COFs using borate linkages have been reported, it has not yet been possible to conduct a single-crystal structural analysis on these COFs."
A tetrahedral framework takes shape
Currently, most crystalline COFs rely on imine linkages, or carbon-nitrogen double bonds, which limit their structural diversity. Exploring new modes of bond formation for crystalline COF synthesis, such as the borate ion linkage motif used by the research team, allows scientists to expand the variety of COFs synthesized and further uncover novel structure-function relationships.
Borate anions contain the elements boron and oxygen, are negatively charged and are commonly used as building blocks in materials science. In the current study, the tetracoordinate spiro-type structures created by the researchers are formed with a central borate anion to which four tetracyclopentatetraphenylene (TCTP) molecules are bound, forming a tetrahedron with a unique 3D shape that can be tuned for different applications.
The research team successfully synthesized a 3D COF with nbo topology, which refers to a highly symmetrical 3D network structure that mimics the crystal lattice of niobium monoxide (NbO), an inorganic compound. These structures are known for their permanent porosity, high thermal stability and large, accessible pores.
The 3D COF with NbO topology the team synthesized, TCTP-COF, is a highly porous material with a crystalline structure and an open lattice. "In this study, we selected TCTP to achieve both a square-planar structure and a monomer unit with sufficient solubility," Segawa said.
Structure solved for future tuning
Importantly, the research team was able to synthesize TCTP-COF and also determine its structure.
"This study not only reports the first structural elucidation of a borate-linked 3D crystalline COF via electron diffraction but also demonstrates the potential of hetero[8]circulene analogs (flat, ring-shaped synthetic molecules) as robust building blocks for complex 3D frameworks. These findings pave the way for both the precise construction of functional ionic COFs and the exploration of their structure-property relationships to enable their use in advanced applications," Segawa said.
Publication details
Soshi Hirota et al, Crystalline 3D covalent organic frameworks with nbo topology, Science Advances (2026). DOI: 10.1126/sciadv.aeg6230. www.science.org/doi/10.1126/sciadv.aeg6230
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Citation: New 3D COF structure could help tune porous materials for batteries and cleanup (2026, July 10) retrieved 11 July 2026 from https://phys.org/news/2026-07-3d-cof-tune-porous-materials.html
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