Directing Cation Coordination and Phase in Nickel Sulfide Nanocrystals through the Addition of Phosphines

In nanocrystal syntheses, multiple routes to achieve phase control have been explored, such as precursor reactivity and cation exchange. While these routes have opened doors to phase manipulation, the former does not directly target the product structure and the latter has limitations on which structures can be formed. Here, we combine both ideas, focusing on the structure and also influencing precursor reactivity. For the first time, we intentionally used concepts from coordination chemistry to influence the metal in solution and, in turn, affect the interstitial sites that the cation fills in the solid. Through the addition of bidentate and monodentate phosphine ligands of varying bite angles, steric bulk, and electron donation ability, we were able to influence the coordination around the nickel ion and thus the product nickel sulfide phase. We discovered that the steric bulk of the phosphine had the biggest influence on the resulting product by destabilizing surfaces with highly coordinated nickel atoms by occupying coordination sites on the metal. By varying which phosphine ligand was added, we were able to selectively target pure millerite (NiS), heazlewoodite (Ni₃S₂), and godlevskite (Ni₉S₈).