Precision Synthesis of Cadmium Selenide Semiconductor Nanoclusters Via Cation Exchange

Precision synthesis at the nanoscale with well-defined precursors, pathways, and products is important for atomic-level engineering of nanomaterials. Despite the importance, the progress in synthesizing atomically precise semiconductor clusters has been a daunting task due to their complex structures and entangled reaction kinetics. Cation exchange reactions have been widely used to access novel colloidal nanocrystals. In this presentation, we will discuss the “precisionalization” of cation exchange reactions to synthesize atomically defined CdSe nanoclusters. Specifically, the reaction of a Cu₂₆Se₁₃(PEt₂Ph)₁₄ template cluster with a CdI₂(PPr₃)₂ cation complex afforded a Cd₂₆Se₁₇I₁₈(PPr₃)₁₀ cluster with near-unity conversion yield. X-ray crystallography shows that the Se₁₃ anion framework in the template cluster is preserved and further enlarged in the product cluster. The surface ligands of the CdSe cluster are fully dictated by the complex precursor. The atomic structures of Cd₂₆Se₁₇ clusters further unveil the origin of charity and polarity of semiconductor nanoclusters. Atomic insights into transformation pathways can be derived based on the in situ absorption spectra and the comparison of the crystal structures. In addition, by changing the ligands in the cadmium complex, a carboxylate-protected CdSe cluster can be produced with a slower transformation rate due to the lower reactivity of Cd(II)-carboxylate precursors. The realization of atomic precision in cation exchange reactions is expected to expand the library of atomically precise semiconductor nanomaterials and further understand their structure-property relationships.