Homogeneous crystal nucleation and growth reactions are often controlled by the slow conversion of molecular precursors. This reaction supplies solute to the crystallization medium leading to supersaturation, nucleation, and growth. The kinetics of solute supply can dictate the number of nuclei that form and therefore the final nanocrystal size, as well as influence the size distribution. Thus to gain reproducible control over nanocrystal size and size distributions, it is crucial to tune and understand precursor conversion kinetics. I will describe a family of substituted thioureas that are conveniently prepared from commercial amines and organoisothiocyanates. Their reaction with metal surfactant complexes produces metal sulfide nanocrystals in quantitative yields at a rate that can be tuned by modifying the organic substituents. A diverse variety of substitution patterns affords reaction rates that vary over several orders of magnitude allowing a desired nanocrystal size to be prepared in quantitative yields. The relationship between the precursor conversion rate and crystal nucleation will be described. I will also describe structural models for nanocrystal nuclei that we have synthesized and structurally characterized using a combination of single crystal diffraction, and pair distribution function analysis of powder x-ray scattering data.

Precursor conversion reactions and the mechanism of nanocrystal nucleation and growth

248th National Meeting (2014)

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