The arrangement of atoms in inorganic crystals has a significant impact on the properties of the material. While organic chemists have established pathways towards target products, solid-state chemists are often limited to obtaining thermodynamic phases, as the high-temperature synthetic methods used to generate solid materials are not easy to rationally manipulate to yield arbitrary structural targets, particularly in systems where multiple polymorphic structures might exist. Nanoscale cation exchange, which proceeds quickly under mild conditions, can engineer the elemental composition of a nanocrystal while preserving key structural features of the template, which can result in the formation of unexpected crystal phases in some cases. However, the predictive power of this chemistry has not been well established, and it has been largely centered on late- and post-transition metal systems. This presentation will highlight the transformation of digenite Cu<sub>2-x</sub>S nanoparticles to zincblende MnS and CoS, crystal structures that are metastable in bulk, through a low-temperature cation exchange process. Importantly, the product structures retain structural characteristics of the digenite starting material; namely, both the cubic closest packed arrangement of anions and the tetrahedrally coordinated cation coordination environment. When combined with analogous exchange chemistry transforming a roxbyite Cu<sub>2-x</sub>S nanotemplate to metastable wurtzite MnS and CoS with similar retention of the seed structure, we demonstrate the rational, predictive power of cation exchange for targeting arbitrary structural features otherwise inaccessible to direct synthetic methods.

Structure-selective cation exchange in the synthesis of zincblende MnS and CoS nanocrystals

254th National Meeting (2017)

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