Coordinated\nAnions Tune Z‑Type Ligand Displacement\nfrom Colloidal CdSe and InP Nanocrystal Surfaces

Neutral metal salts coordinate to the surfaces of colloidal\nsemiconductor\nnanocrystals (NCs) by acting as Lewis acid acceptors for the NC surface\nanions. This ligand coordination has been associated with increased\nemission due to the passivation of surface hole traps. Here, variation\nof the anionic ligands of metal salts is used to study anion effects\non metal complex Lewis acidity and surface coordination at CdSe and\nInP NCs. To resolve dynamic ligand exchange processes, the tetracarbonylcobaltate\nanion, [Co(CO)<sub>4</sub>]<sup>−</sup>, is used as a monoanionic\nligand for which IR spectroscopy can readily identify displacement\nof neutral M[Co(CO)<sub>4</sub>]<sub><i>x</i></sub> species\n(M = Cd or In; <i>x</i> = 2 or 3, respectively) upon addition\nof neutral donor ligands. Notably, although Cd[Co(CO)<sub>4</sub>]<sub>2</sub> is more Lewis acidic than cadmium oleate, the former is more\nreadily displaced from the NC surfaces. Lewis acidity and X-type anion\nexchange are, therefore, factors to be considered when performing\npostsynthetic addition of metal salts for NC photoluminescence emission\nenhancement.