Publication date: 15th May 2025
There is a huge diversity of transaction metal chalcogenides, varying in composition and symmetry. When we put reagents in the flask for colloidal synthesis, how do we select for one crystalline phase over another? I will discuss our work with transition metal sulfides and selenides to answer these questions. We use libraries of reagents and ligands to examine kinetic and surface chemistry effects, and careful analysis of the molecular transformations that preclude nanocrystal formation and growth. Or main lessons have been:
1) Ligands change the rules of the game before it even starts.
Often ubiquitous ligands react with our reagents before nanocrystal formation, changing their nature, which in turn influences the final crystalline phase.
2) Structural motifs of the first nucleated phase are often retained in the product phase, even if the stoichiometry is different. Understanding the structural relationships between phases such as cation coordination or anion stacking patterns can be used, in concert with chemical potential and the nucleating phase, to rationally develop syntheses to each of the phases in a family.
3) The structural motif of cation coordination number on the crystal surface can be influenced by ligand coordination. The motif can become translated through the nanocrystal, controlling phase.
4) The over-growth and isolation of metastable polytypes require slow reaction conditions. Diffusion of reagents through the ligand shell is one route.
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