Coordination nanosheets are a unique class of two-dimensional (2D) materials that are formed by coordination bonds between planar organic ligands and metal ions. These 2D nanomaterials are increasingly utilized in energy storage, electronic devices, and as electrode-based catalysts due to their excellent electronic, optical, redox properties, and catalytic activity. Over the last decade, coordination nanosheets composed of various transition metal ions, such as nickel (Ni) ions linked to benzenehexathiol (BHT)—an organic compound—have been successfully synthesized in laboratories. However, their production has relied on a two-phase interfacial reaction that occurs between two immiscible phases of matter.
Furthermore, the selective synthesis of well-organized heterometallic nanosheets, containing two or more metal ions, has proven to be difficult. To address these two major issues limiting the production of novel coordination nanosheets, a team of researchers led by Professor Hiroshi Nishihara, from the Research Institute for Science and Technology (RIST), Tokyo University of Science (TUS), Japan, has conducted a series of innovative experiments. The research team comprised Ms. Miyu Ito, a Master's student at TUS, project researchers Dr. Naoya Fukui and Dr. Kenji Takada, and Dr. Hiroaki Maeda, a lecturer at TUS. Their findings were published online in the journal Small on May 05, 2025, and selected as the Front Cover of the issue.
“When Ni ions are used in the two-phase interfacial reaction, porous nickelladithiolene (NiDT) and non-porous NiBHT structures are obtained. However, a rational method for selectively synthesizing them has not been fully established until now,” says Prof. Nishihara, explaining the motivation behind the present study.
The researchers employed a single-phase reaction of Ni2+ ions and BHT to form colloidal solutions of coordination nanosheets. Notably, by controlling the molar ratio of Ni2+ ions and BHT, the researchers could selectively synthesize coordination nanosheets of interest in a single-phase reaction. The prepared colloidal coordination nanosheets can be further utilized as inks to coat substrates or electrodes, or as solutions for subsequent chemical reactions.
To validate the utility of coordination nanosheets in colloidal solutions, the researchers coated glassy carbon (GC) with NiDT and NiBHT. During subsequent electrochemical analysis, NiDT showed a broad redox wave, indicating a porous structure, while non-porous NiBHT did not show a redox wave at the corresponding potential. Further testing of the NiDT-coated GC electrode revealed a high potential for the hydrogen evolution reaction as a catalyst.
Drawing inspiration from their research findings, the team successfully synthesized colloidal nanosheet solutions containing copper (Cu) linked to BHT and zinc (Zn) linked to BHT. Furthermore, by adding Cu2+ ions to the NiDT colloidal solution containing unreacted BHT, they were able to generate NiCu2BHT nanosheets, where the Cu2+ ions could be introduced into the pores of NiDT. Through a similar strategy, coordination nanosheets of NiZn2BHT, new compounds were prepared by introducing Zn2+ ions into NiDT colloidal solution.
In addition to using colloidal solutions, the researchers turned their attention to a transmetallation reaction—a type of organometallic reaction where metal ions at the coordination center are replaced with other ions to produce heterometallic coordination nanosheets. Remarkably, the first step of the transmetallation reaction of NiBHT with Cu2+ metal ions resulted in NiCu2BHT nanosheets.
“NiCu2BHT has high crystallinity and electrical conductivity and can be utilized in diverse electronic applications. This shows the superiority of the structure and physical properties of heterometallic coordination nanosheets with a defined structure,” states Prof. Nishihara.
Taken together, this study reveals two novel synthesis routes to produce highly conductive coordination nanosheets in an ink-like form, which can be further applied as coatings to various substrates and used as chemical reactants.
Prof. Nishihara concludes by highlighting the future applications of the present research, “The first ink made from coordination nanosheets has made it possible to mass-produce them using printing technology and to apply them directly to devices, marking a major step forward in their practical use as next-generation flexible electronic devices, hydrogen production catalysts, and sensor materials.”
Thanks to the researchers of TUS, the promise and potential of low-cost, high-performance nanomaterials can be realized, leading to a sustainable and energy-efficient society.
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Reference
DOI: 10.1002/smll.202503227
About The Tokyo University of Science
Tokyo University of Science (TUS) is a well-known and respected university, and the largest science-specialized private research university in Japan, with four campuses in central Tokyo and its suburbs and in Hokkaido. Established in 1881, the university has continually contributed to Japan's development in science through inculcating the love for science in researchers, technicians, and educators.
With a mission of “Creating science and technology for the harmonious development of nature, human beings, and society," TUS has undertaken a wide range of research from basic to applied science. TUS has embraced a multidisciplinary approach to research and undertaken intensive study in some of today's most vital fields. TUS is a meritocracy where the best in science is recognized and nurtured. It is the only private university in Japan that has produced a Nobel Prize winner and the only private university in Asia to produce Nobel Prize winners within the natural sciences field.
Website: https://www.tus.ac.jp/en/mediarelations/
About Professor Hiroshi Nishihara from Tokyo University of Science
Professor Hiroshi Nishihara currently serves as the specially appointed Vice President of Tokyo University of Science, Japan. His main research interests include coordination chemistry, electrochemistry, photochemistry, and nanoscience. Over the years, he has published 475 scientific papers that have been cited more than 18,470 times. In addition to developing six patents, he has received prestigious awards and honors, including the Angewandte Chemie Cover Picture Award for his research excellence. He is also an honorary member of multiple academic societies, such as the Royal Society of Chemistry and The Electrochemical Society of Japan.
Funding information
This work was financially supported by JSPS KAKENHI (Grant Numbers: JP19H05460, 22K14569, 22K05055, 24H00468, 25K08421, and 25K08598) and the White Rock Foundation.
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