Istruzione e Formazione
Kanazawa University Research: Metallic complexes made from cyclic molecules
The scientists first discuss the origins of the field. In the 1970s, it was shown that so-called [2+2] macrocycle dinuclear complexes could be formed by using a relatively simple organic compound, with molecular formula C H O , as the building block. These dinuclear complexes consist of two metal atoms sitting in an organic 'web' with 2-fold symmetry. Similar Robson macrocycles, as they are called, can be obtained with 6 metals, with the overall [3+3] structure having 3-fold (triangular) symmetry. Robson macrocycles are still researched today, but the method remains somewhat unpredictable.
The researchers then explain how [2+2] (with two-fold symmetry) and [3+3] (with triangular symmetry) macrocycles also feature in contemporary designs. The [3+3] compounds are nowadays actively researched because of their potential as single-molecule magnets — molecules that exhibit (para)magnetism. Using macrocycles, the magnetic properties of the ensuing molecules can be tuned by changing cluster size and composition. Regarding the [2+2] complexes, these are noted to have cavities that can be exploited for creating unique clusters.
Another interesting class of multimetallic structures are the 'Pacman macrocycles', built from ligands displaying a cleft. This geometry can be used to capture and activate small metal–ligand–metal molecules. In this context, Pacman macrocycles with two uranium atoms have been intensively studied in the context of nuclear waste processing. Akine, MacLachlan and Chaudhry also show that, more generally, by using Pacman ligands, chemists have succeeded in making several structurally and chemically unique polymetallic complexes.
The final type of macrocycles discussed by the researchers features pyridine rings (pyridine is similar to benzene, with one C–H unit replaced by nitrogen). Pyridine-ring macrocycles offer high flexibility, and can be used to synthesize a variety of complicated multimetallic structures — the authors give plenty of examples of silver-containing complexes.
The scientists finish their review with an outlook of this fascinating research area. Specifically, they note that a future trend is likely to be the mimicking of the activity of naturally occurring clusters in living systems. Indeed, polymetallic complexes play key roles in important reactions such as the reduction of nitrogen to ammonia and the oxidation of carbon monoxide to carbon dioxide. Quoting Chaudhry : "The potential selectivity and control rendered by the macrocycle-templating method is especially attractive for consistent, reproducible production of functional multimetallic clusters."
https://nanolsi.kanazawa-u.ac.jp/wp-content/uploads/2021/09/fig1.jpg
Figure 1. Contemporary macrocycles used for the synthesis of discrete polymetallic complexes: (a) concept, (b) chemical structures of representative polymetallic complexes.
Mohammad T. Chaudhry ,
Shigehisa Akine , and Mark J. MacLachlan . Contemporary macrocycles for discrete polymetallic complexes: precise control over structure and function,
DOI https://doi.org/10.1039/D1CS00225B
Hiroe Yoneda
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As the leading comprehensive university on the Sea of Japan coast, Kanazawa University has contributed greatly to higher education and academic research in Japan since it was founded in 1949. The University has three colleges and 17 schools offering courses in subjects that include medicine, computer engineering, and humanities.
The University is located on the coast of the Sea of Japan in Kanazawa – a city rich in history and culture. The city of Kanazawa has a highly respected intellectual profile since the time of the fiefdom (1598-1867). Kanazawa University is divided into two main campuses: Kakuma and Takaramachi for its approximately 10,200 students including 600 from overseas.