Hiroyuki Isobe, Professor, Department of Chemistry

Kohki Ikemoto, Lecturer, Department of Chemistry

Key points of the presentation

• The "twin brother of diamond (PORX)" appeared in a chemical synthesis. Pollux is a new material that has the same "perfect symmetry" and "strong isotropy" as diamond, and also has a unique "chirality," but until now it has been a theoretical or imaginary material.
• In this research, we designed and synthesized the "smallest cage unit of poluxenes" called poluxenes.
• The chemical synthesis has revealed the unique "chirality" characteristics of poluxenes.

 

Announcement Summary

A research group led by Professor Hiroyuki Isobe of the Graduate School of Science, The University of Tokyo, has made the world's first appearance of "Pollux," a twin brother of diamond, through chemical synthesis (Figure 1). They designed and synthesized the molecule "Polluxen," the smallest cage unit cut out from Pollux, which has the same "perfect symmetry ^{(Note 1)" and} "strong isotropy ^{(Note 2)} " as diamond (Figures 2 and 3). It was theoretically known that polux has a unique chirality ^{(Note 3)}, which is different from that of diamond, but this research enabled the structural analysis of poluxene as a real substance for the first time and clarified part of its complex chirality characteristics. These results are expected to lay the foundation for the development of new chiral nanocarbon materials in the future.

The research results were published in the international journal "Proceedings of the National Academy of Science, U.S.A. (PNAS )" on February 8, 2022.

 

Publication details

The beauty of diamonds attracts many people, but the beauty of their structure also fascinates scientists. For example, the smallest cage unit of diamond is known as adamantane, and its theoretical prediction in 1905/1924, isolation from crude oil in 1933, the first chemical synthesis in 1941, and the establishment of a simple mass synthesis method in 1957 have greatly advanced research in the fields of physics and chemistry. The beauty of the diamond structure has been mathematically elucidated very recently, and it has been proposed that the three-dimensional space is filled with carbon atoms in such a way that it has "perfect symmetry" and "strong isotropy". Based on the mathematical approach that clarified "perfect symmetry" and "strong isotropy," it was proposed in 2008 that there can be only one more carbonaceous material with "perfect symmetry" and "strong isotropy" other than diamond. In fact, the unique network structure of this dream new material, the "twin brother of diamond," has a long history and has been the subject of frequent theoretical studies since its first proposal in 1932, and has been given various names (Laves' net, Net 1, Y*, net (10,3)-a 3/10/c1, srs, double triamond, _K4). One of the reasons this network has attracted widespread interest is the presence of a unique "chirality" not found in diamonds.

However, until now, the "diamond's twin brother composed of carbon" has been a theoretical and imaginary material, and its unique network structure has never existed as a real material that can be handled (Figure 1).

Figure 1: Pollux and Polluxen (smallest cage unit in orange). Polluxen, shown in orange, was chemically synthesized.

 

The research team has successfully chemically synthesized the smallest cage unit of these "diamond twin brothers" (Figures 2 and 3). The research team also named the infinite-length carbon network Pollux and the smallest cage unit Polluxene, after the Gemini twin brothers of Castor and Pollux in Greek mythology.

Figure 2: Polluxene. Side view of the crystal structure of chemically synthesized poluxene.

Figure 3: Polluxene. Crystal structure of chemically synthesized poluxene, viewed from above.

 

The polxene is the smallest cage unit that maintains the symmetry of the porcus, and in this study, a new design was conceived that places benzene rings at the 14 vertices of the cage structure. The original porcus was proposed as a network of ^sp2-mixed carbons in a planar triangular basic structure, and the idea was to replace it with a benzene ring. Based on this idea, the research group has succeeded in the chemical synthesis of polxene by linking 14 benzene rings at the vertex with 15 carbon-carbon bond edges (Figures 2 and 3). In this synthesis, three types of reactions called aromatic coupling reactions were utilized, all of which are "Japan-originated" coupling reactions, and a simple and efficient synthetic method was realized.

In this research, we have further succeeded in unlocking the secret of the "chirality" of Pollux-Poluxen. It had been proposed that there existed a counter-palpability or chirality in the Pollux network, which is a mirrored relationship like "right hand/left hand". In this study, the research group synthesized Polksen's "without chirality" and "with chirality" separately, and further conducted theoretical and mathematical analysis. As a result, it was found that there are very complicated stereoisomers ^{(Note 4)} in the structure of Pollux-Poluxen, and the possible structures of the smallest cage unit are as many as 5600 species. Then, a method to fix chirality was devised, and two chiral species in a mirror-image relationship were chemically synthesized, and each was successfully isolated as a chiral substance.

The chemical synthesis of the imaginary substances "Pollux" and "Polluxen" is expected to contribute to the development of nanocarbon materials in the future. In particular, the existence of complex stereoisomerism and chirality has been demonstrated, which is expected to attract more attention as a chiral material.

This research was conducted as part of a Grant-in-Aid for Scientific Research.

 

Name of Researcher	Affiliation
Toshiya Fukunaga	Graduate Student, Graduate School of Science, The University of Tokyo
Takahide Kato	Graduate Student, Graduate School of Science, The University of Tokyo
Kohki Ikemoto	Lecturer, Graduate School of Science, The University of Tokyo
Hiroyuki Isobe	Professor, Graduate School of Science, The University of Tokyo

 

 

Journal

Journal name	Proceedings of the National Academy of Sciences of the United States of America (PNAS)
Title of paper	A minimal cage of a diamond twin with chirality （A minimal cage of a diamond twin with chirality)
Author(s)	Toshiya M. Fukunaga, Takahide Kato, Koki Ikemoto* & Hiroyuki Isobe* (authors)
DOI Number	10.1073/pnas.2120160119
URL	http://dx.doi.org/10.1073/pnas.2120160119