Structural transformations are ubiquitous at all length scales in chemistry, spanning from isomerization reactions of small molecules to solid-solid transformations in bulk crystals, which have generally been studied in isolation. Despite attempts to merge understanding of these disparate regimes by reducing domain size in solids to nanocrystalline dimensions, bulk-like solid-solid transformation behavior still predominates at length scales approaching those of molecules. In-between small molecules and nanocrystals, magic-sized clusters (MSCs) provide an advantageous experimental platform to study isomerization in well-defined atomically precise systems. We show here that a reversible transformation between CdS cluster isomers with distinct stable configurations possesses essential characteristics of both solid-solid transformations and molecular isomerization reactions. These isomers, termed α- and β-(Cd2S)x, interconvert (α-to-β/β-to-α) reversibly, as identified by a 140 meV shift in the species’ excitonic energy gap. A characteristic displacive reconfiguration of the inorganic core (solid-solid transformation), as evidenced by our reconstruction of the atomic pair distribution function from x-ray scattering, accompanies the change in electronic structures. The first order kinetics of the transformation—indicative of molecular isomerization—are driven by a distortion of the ligand binding motifs due to the presence of hydroxyl species in the ligand shell. Chemical control over the surface energy boundary conditions via adsorbates appears to be the exclusive determinant of “phase” stability in this system. The reversible transformation of MSCs reported here presents the missing bridge between molecular isomerization and solid-solid transformations. Manipulation of MSCs, which serve as seeds and as a monomer reservoir in nanocrystal growth, will provide an additional strategy for control over the structure of colloidal nanocrystals.

Chemically reversible isomerization in inorganic magic sized clusters

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.