Multiscale Isomerization of Magic-Sized Inorganic Clusters Chemically Driven by Atomic-Bond Exchanges

The recent discovery of chemically reversible isomerization of CdS clusters (Williamson et al. Science2019, 363, 731) shows that the structural transformation of such inorganic clusters has essential characteristics of both small-molecule isomerization and solid–solid transformation. Despite its importance in synthesizing colloidal quantum dots from cluster intermediates (so-called "magic-sized clusters" or MSCs), the underlying mechanism for such inorganic isomerization is not yet understood. Here, using ab initio simulated spectroscopy, we propose a microscopic mechanism for the multiscale isomerization of CdS MSC. When triggered by hydroxyl adsorption, a carboxylate-ligated CdS cluster undergoes a structural transformation through Cd–S bond exchanges at the bond-length scale (molecular isomerization), which induces the change in the stacking sequence of the partially ordered CdS lattice (solid–solid transformation). The creation of the bond-exchange defects in the CdS core and "self-healing" by ligand rearrangements on the surface play a central role in the isomerization. MSCs can be thus made susceptible to forming a particular type of point-like defect (e.g., bond-exchange defect), which provides useful insights into understanding the stability and structural activation of MSCs.