Successful Development of Asymmetric Alloying Method for Carbon-Centered Gold(I) Ion Clusters: Chiral Alloy Clusters Emitting Light in the Red to Near-Infrared Regions

【Research Summary and Highlights】

By adding a silver salt to a gold(I) ion cluster containing six gold(I) ions bound around a central carbon ion, a racemate of chiral carbon-centered gold(I)-silver(I) alloy clusters was obtained. This process involved the introduction of silver(I) ions (alloying) and a reduction in the number of gold(I) ions (etching). Furthermore, by adding a homochiral carboxylic acid, asymmetric alloying was successfully achieved, resulting in the formation of optically pure alloy clusters.

The aforementioned alloy clusters exhibited long-lived phosphorescence in the red to near-infrared regions. The homochiral alloy clusters showed circular dichroism and circularly polarized luminescence. The nature of their bonding and the mechanism of their luminescence were clarified through theoretical calculations.

This research presents an excellent synthesis method for homochiral alloy clusters based on asymmetric alloying through the introduction of different metal ions and etching. It is expected to contribute to the creation of chiral luminescent nanomaterials and applications in the field of optical functional materials.

【Research Overview】

A joint research team led by Professor Mitsuhiko Shionoya, Assistant Professor Pei Xiao-Li, and Lecturer Hitoshi Ube from the Tokyo University of Science; Professor Masahiro Ehara and Project Assistant Professor Zhao Pei from the Institute for Molecular Science; and Professor Lei Zhen and graduate student Liu Wen-Ting from Fuzhou University, successfully synthesized chiral alloy clusters consisting of carbon-centered gold(I) and silver(I) ions. They achieved asymmetric alloying using a homochiral carboxylic acid and clarified the luminescence properties of these clusters in the red to near-infrared regions.

Specifically, by adding silver trifluoroacetate to a carbon-centered hexanuclear gold(I) ion cluster (CAuI6) protected by triphenylphosphine ligands with high structural symmetry, they discovered that a racemate of carbon-centered gold(I)-silver(I) alloy clusters (CAuI4AgI6) with a bicapped square antiprismatic polyhedron structure is obtained. This occurs via the introduction of silver(I) ions and the etching of gold(I) ions. Additionally, the addition of a homochiral carboxylic acid successfully led to asymmetric alloying, constructing homochiral alloy clusters. These alloy clusters exhibited long-lived phosphorescence in the red to near-infrared regions. The homochiral alloy clusters demonstrated circular dichroism and circularly polarized luminescence, with their bonding characteristics and emission mechanisms elucidated by theoretical calculations.

This study proposes a highly efficient and selective synthesis method for metal ion clusters based on asymmetric alloying, which involves the introduction of different metal ions and etching. The findings are expected to contribute significantly to the development of chiral luminescent nanomaterials and the field of optical functional materials.

These research results were published online in the international academic journal "Nature Communications" on June 5, 2026.

【Detailed Research Results】

Luminescent metal ion clusters exhibit precise control over the arrangement of metal ions depending on the types and compositions of ligands and metal ions that stabilize the overall structure and contribute to its properties. This precision results in unique physical properties and reactivities inherent to their structures. In this study, researchers focused on the unexplored area of alloying at the single-atom level and controlling chirality in sub-nanometer-sized metal ion clusters. Previously, the primary method for imparting chirality to metal clusters was the external introduction of homochiral ligands. Conversely, alloying by adding achiral metal salts to impart intrinsic chirality to the metal core itself had rarely been reported. Therefore, this study aimed to develop a method for synthesizing chiral metal clusters as racemates through alloying, as well as highly selective synthesis of homochiral alloy clusters via asymmetric induction using homochiral carboxylic acids.

Specifically, by adding silver trifluoroacetate to the highly symmetrical carbon-centered gold(I) ion cluster (CAuI6) protected by triphenylphosphine ligands, alloying was achieved involving the introduction of six silver(I) ions and the etching of two gold(I) ions. This resulted in the synthesis of a racemate of a carbon-centered gold(I)-silver(I) alloy cluster (CAuI4AgI6) possessing a bicapped square antiprismatic polyhedral structure. By further adding a homochiral carboxylic acid to this racemate, the team succeeded in asymmetric alloying, enabling the synthesis of the alloy cluster with high diastereoselectivity in a short process. Single-crystal X-ray structural analysis of the racemate revealed that four gold(I) ions and six silver(I) ions are asymmetrically arranged at the vertices of a bicapped square antiprismatic structure featuring a carbon center. Furthermore, the symmetry of this structure is reduced to a pseudo-D2 symmetry.