Structural Isomerism in Atomically Precise Nanoclusters

Molecular isomerization has been well established in small-sized organic molecules, whereas bulk inorganic solids present the phase transformation. Studies of molecular isomerization and phase transformation have thus far proceeded largely independently. Significantly, the nanocluster-based structural isomers occupy the boundary between molecular isomerization and phase transformation—they serve as small-size nanoparticles but display the molecule-like isomerization rather than the bulk-like phase transformation. The subject of structural isomerism has emerged recently as a new "growth point" in the nanocluster science. In this Review, we highlight the advances in researching the structural isomerism of atomically precise nanoclusters. We first discuss the geometric structures of nanocluster structural isomers. Nanocluster quasi-structural isomers are then reviewed. The factors that account for the structural isomerism and the interconversions between nanocluster isomers are disclosed as well. Then, we elaborate on the structure-dependent properties of these nanocluster structural isomers and highlight the ligand effects on structures and properties. Finally, the present challenges in studying the nanocluster structural isomerism, as well as some personal perspectives toward this research direction, are proposed. This review hopefully provides researchers attempting to study the nanocluster structural isomerism with a researching fundamental.