A Chiral CdS Magic-Size Cluster with Enantiomerically-Biased Crystallization

Despite the symmetric, achiral atomic lattices typically found in binary semiconductor nanocrystals, we show that during their early formation stages, especially in the magic-size cluster (MSC) regime, chirality can be present in these metastable, transient species, which are capable of further self-assembling into high-level chiral superstructures. Through a cation exchange process operating at room temperature, a structurally symmetrical copper sulfide cluster has been successfully converted into a pair of enantiomeric cadmium sulfide MSCs, formulated as Cd28S17I22(PEt3)12 (abbreviated as (+)/(-)-[Cd28S17]). The atomic structures of these two MSCs were established by single-crystal X-ray crystallography. It is revealed that the [Cd28S17] MSCs feature an antisupertetrahedron configuration which has never been observed in reported CdS structures. Remarkably, rather than crystallizing into a racemic mixture, (+)/(-)-[Cd28S17] MSCs naturally crystallize out in an enantiomerically biased manner, sufficiently rendering distinctly opposite chiroptical responses. This behavior reflects genuine circular dichroism activity, which can be directly attributed to the chiral atomic structure of this well-known quantum photonic nanomaterial.