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A metal cluster is an association of several metal atoms, between which there is a significant interaction. Clusters that consist of atoms of different metals are called heterometallic — they can be catalysts in organic reactions, for example in pharmaceuticals and polymer production. However, creating such clusters is not easy. The chemists of RUDN and INEOS described how it is possible to efficiently produce heterometallic clusters from an “ordinary” metal cluster consisting of three rhodium atoms.

“Rhodium is well known as a catalytic metal. There are many organic processes that are catalyzed by rhodium-based metal clusters. However, most approaches for the synthesis of heterometallic clusters are random and give a low yield of the desired product. We managed to create heterometallic clusters of rhodium with high reaction efficiency,” says Olga Chusova, PhD, researcher at the research center “Crystal Chemistry and Structural Analysis” of the RUDN University.

The chemists used a cluster of three rhodium atoms that join together to form a triangle. Ligands — molecules that dictate the behavior of rhodium atoms — are attached to the vertices and sides of this triangle. The detailed selection of ligands in both the initial cluster and the reagents allowed chemists to create new heterometallic clusters. The fact is that compounds feel better with some ligands than with others. In this case, the addition of metalloelectrophil as a reagent, which contains an atom of another metal with a lack of electrons, made it possible to create a new complex that consists of atoms of different metals — a heterometallic cluster. Instead of a triangle, a tetrahedron is formed — at its vertices three rhodium atoms and another gold or cobalt atom.

Such a mechanism provided almost one hundred percent efficiency of the reaction — that is, the actual amount of the obtained heterometallic cluster almost coincided with the theoretically calculated one (81% of the theoretical value for the cluster with cobalt and 93% — with gold). It is noteworthy that it worked equally well, despite the fact that metalelectrophiles with gold and with cobalt have different structures.

“Although metalloelectrophiles have different electronic structures, they both react with a triangular rhodium cluster and form stable tetrahedral clusters. This phenomenon is due to the unique structure of the original rhodium cluster, as it can provide a different number of electrons depending on the needs of the metalelectrophile. In this case, the gold derivative needed only two electrons to achieve the dream, and the cobalt derivative needed as many as six,” says Olga Chusova.

According to scientists, the discovery will increase the efficiency of the synthesis of catalysts based on heterometallic clusters for the chemical industry.

The study is published in the .