Tolman’s Electronic Parameter of the Ligand Predicts Phase in the Cation Exchange to CuFeS₂Nanoparticles

The metastable and thermodynamically favored phases of CuFeS₂ are shown to be alternatively synthesized during partial cation exchange of hexagonal Cu₂S using various phosphorus-containing ligands. Transmission electron microscopy and energy dispersive spectroscopy mapping confirm the retention of the particle morphology and the approximate CuFeS₂ stoichiometry. Powder X-ray diffraction patterns and refinements indicate that the resulting phase mixtures of metastable wurtzite-like CuFeS₂ versus tetragonal chalcopyrite are correlated with the Tolman electronic parameter of the tertiary phosphorus-based ligand used during the cation exchange. Strong L-type donors lead to the chalcopyrite phase and weak donors to the wurtzite-like phase. To our knowledge, this is the first demonstration of phase control in nanoparticle synthesis using solely L-type donors.