Phases, polytypes and polymorphs: how to make what you want in nanocrystal synthesis Janet Macdonald 1,2 , Jeremy R. Espano 1 , Andrey A. Shults 1,2 , Alexandra C. Koziel 1,2 , Danielle N. Penk 1,2 , Antony R. Peng 1,2 , Eric Ho 1,2 , Emma J. Endres 1,2 , Ahmed Y. Nuryie 3 , Guanyu Lu 2,4 , Joshua D Caldwell 2,4 1 Department of Chemistry, Vanderbilt University, Nashville, USA 2 Vanderbilt Institute for Nanoscale Science and Engineering, Nashville, USA 3 Department of Chemistry, The Pennsylvania State University, Abington, Pennsylvania, USA 4 Department of Mechanical Engineering, Vanderbilt University, Nashville, USA When nature provides multiple options of compound materials, how and why does one crystalline phase form over another in a synthesis? The literature is rife with phenomenological observations of synthetic conditions that give certain phases. In truth, as scientists, we do not have the synthetic tool kit to a priori imagine a synthesis that selects for one natural geological phase over another, nor rationally tweak a “failed” reaction to achieve a goal phase. Without this knowledge, it is very hard to imagine we can synthesize, study, and exploit the full potential of the periodic table in crystalline materials. Two projects aimed at creating such a tool kit will be presented. A library of substituted thioureas reagents were used as a way to study isolate the effect of the kinetics of the release of sulfur on the phase of iron and cobalt sulfides. These studies illuminated the paths how the metal sulfides transform into each other. Specifically, the anion packing pattern of ccp or hcp in the nucleated phase is the key determining factor of the family of phases produced through further sulfur inclusion. The knowledge of the relationships between the phases was used to identify conditions to selectively synthesize phase pure samples of many of the cobalt and iron sulfides. One of the main challenged with nanocrystal synthesis is we don't often know what is happening at the molecular level. Phase and polytype control is very conditions dependent. In the second part I will describe how we are using 1 H and 77 Se NMR to peer into the "black box," and finding out exactly why small changes in reagent, ligand identify, ligand concentration, and solvent are influencing phase. References 1. Espano, JR; Macdonald JE " Phase Control in the Synthesis of Iron Sulfide" Journal of the American Chemical Society , 2023, accepted. Shults, AA; Lu, G; Caldwell, JD, Macdonald JE " Role of Carboxylates in the Phase Determination of Metal Sulfide Nanoparticle" Nanoscale Horizons , 2023, accepted Penk, DN; Endres, EJ; Nuriye, AY; Macdonald JE "Dependence of Transition-Metal Telluride Phases on Metal Precursor Reactivity and Mechanistic Implications" Inorganic Chemistry, 2023, 62, 9, 3947-3956. 2. Koziel, A; Goldfarb, R; Endres, E; Macdonald, JE"Molecular Decomposition Routes of Diaryl Diselenide Precursors in Relation to the Phase Determination of Copper Selenides" Inorganic Chemistry, 2022, 61, 14673-1683 Ho, EA; Peng, AR; Macdonald JE “Alkyl Selenol Reactivity with Common Solvents and Ligands: Influences on Phase Control in Nanocrystal Synthesis” Nanoscale , 2021, 22, (14), 76-85.
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