Ligand Electronic Properties Dictate Composition of Ni-Based Nanocrystals

Colloidal nanocrystals (NCs) composed of transition metals are appealing for several applications, particularly for those related to their catalytic and magnetic properties. Yet, the chemical principles governing their synthesis remain underexplored compared to other classes of materials. In this study, we take inspiration from molecular inorganic chemistry and implement a systematic ligand screening strategy to elucidate ligand-induced effects in the synthesis of Ni-based NCs. Specifically, we investigate the impact of organo-pnictide ligands with varying steric and electronic properties (i.e., PR₃, AsR₃, SbR₃) in the synthesis of nickel, nickel phosphide, nickel arsenide and nickel antimonide NCs. Using a multimodal characterization approach, we reveal that the electronic properties of the ligands critically determine the resulting NC composition: weak σ-donor ligands promote the formation of nickel pnictides NCs via Ni-E cluster intermediates (E = P, As, Sb), while strong σ-donor ligands favor the formation of metallic Ni NCs via a Ni(I) complex intermediate. We explain the ligand-induced reaction pathways via the reducibility of the Ni center. In addition to fundamental chemical insight, this approach enables the synthesis of a diverse library of colloidal Ni-based NCs, including multiply twinned, flower-like, and cubic Ni NCs, as well as Ni₂P, Ni₁₂P₅, Ni₅P₂, Ni₅As₂, and NiSb NCs. Notably, we synthesize four previously unreported Ni-based NCs: multiply twinned Ni NCs, flower-like Ni NCs, Ni₅P₂ NCs, and Ni₅As₂ NCs. This systematic ligand-based approach provides a robust framework for tailoring and understanding the synthesis of transition metal NCs and beyond.