From intrinsic structures to supramolecular organization: exploring the diversity and origins of chirality in metal clusters

Abstract

Nanoscale chirality has emerged as a dynamic and expanding field of research, with particular emphasis on systems that exhibit optical activity in both the ground and excited states, enabling promising prospects in areas such as enantioselective catalysis, circularly polarized photonics, advanced bioimaging, anti-counterfeiting technologies, and optical data encryption. In contrast to larger nanoparticles, where surface irregularities often complicate the correlation between structure and properties, atomically precise metal clusters serve as accurate model systems in which chiral features can be directly correlated with atomic-level arrangements and electronic structures. Recent developments have uncovered several distinct mechanisms through which chirality manifests in these systems. These include: (i) intrinsic asymmetry within the metal core, or asymmetric orientation of achiral ligands, originating from optically inactive starting atomic configurations; (ii) chirality introduced via optically active surface protecting ligands, where chiral organic molecules transfer or enhance handedness through steric constraints and electronic coupling at the metal–ligand interface; and (iii) supramolecular organization, wherein individual clusters assemble into helically ordered or anisotropic architectures that exhibit collective chiroptical activity. This review brings together these diverse origins of chirality to offer a comprehensive understanding of their structural and physico-chemical bases. Moreover, we highlight how the three distinct origins of chirality in metal clusters differ in their synthetic accessibility and their typical impact on chiroptical behaviour. By putting forth such a perspective, the effort aims not only to advance the fundamental understanding of the mechanisms underlying chirality at the nanoscale, but also to build conceptual frameworks crucial for directing the development of next-generation chiral nanomaterials with tailored characteristics.