Research

The number of atoms that make up a molecule can be described somewhat loosely. For example, when counting metal atoms, we can use numbers like 1, 2, and so on for a few atoms, but when the count increases, it becomes complicated to classify them based on the number. Instead, we start referring to them as clusters or, when they get even larger, as "nano" particles (such as nanoparticles). So, the term "cluster" refers to a group of molecules that falls between individual atoms and "nano" particles, as illustrated left.

In nature, various clusters composed of different metals play crucial roles in important biological functions such as electron transfer and enzymatic reactions. Specifically, when it comes to efficiently carrying out challenging reactions like reducing nitrogen (N2) to ammonia  (NH3) or oxidizing water (H2O) to produce oxygen (O2), clusters that involve multiple metals working together are indispensable. However, we still don't have a clear answer to the question of why and how clusters function. We aim to create these key clusters that hold the answers to such reactions and unravel the mysteries of enzymes. Our goal is to explore functionalities beyond enzymes. For example, the enzyme nitrogenase utilizes a complex cluster consisting of iron and sulfur to reduce N2. Through our unique methods, we are synthesizing model clusters and starting to demonstrate, through experimental chemistry, that nature doesn't rely on magical tricks but operates through mechanisms that can be explained using the language of chemistry. We have also discovered that similar iron-sulfur clusters can directly convert carbon dioxide (CO2) and carbon monoxide (CO) into hydrocarbons, which can serve as fuels. We have high expectations that by advancing this technology, it may become possible to create a fuel regeneration cycle that directly produces gasoline from CO2.

Metal clusters obtained by aggregating metal atoms exhibit significantly different properties compared to bulk metals, nanoparticles with sizes of a few nanometers or larger, and complexes consisting of only one or two metal atoms. These properties can be greatly altered by slight modifications in structure, composition, and atomic arrangement. Currently, known metal clusters are predominantly limited to stable and low-reactivity metals such as gold, silver, and copper. However, in order to pursue unknown functionalities, it is necessary to explore the uncharted territory in the periodic table. We are developing reactions that allow precise control over metal atoms, starting with iron and cobalt, to assemble them into desired structures.

Among the metal clusters obtained through "materials synthesis," iron clusters, for example, can be regarded as compounds that combine the characteristics of enzymes responsible for reducing N2 and the active species of industrial catalysts. In fact, we have achieved catalytic reduction of N2 through these clusters. Furthermore, our "materials synthesis" approach has the potential to lead various metals, beyond iron and cobalt, to form clusters with diverse sizes and structures. We believe that this approach could serve as a universal method for exploring new reactivity and discovering new properties.