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.