title: Tight Binding of Carboxylate, Phosphonate, and Carbamate Anions to Stoichiometric CdSe Nanocrystals.
abstract: To completely displace the carboxylate surface ligands from cadmium selenide nanocrystals, oleic acid impurities are first removed using dimethylcadmium or diethylzinc. In addition to metal carboxylate and methane coproducts, reactions with CdMe2produce surface bound methyl groups (δ = 0.4 ppm, 0.04-0.22 nm-2) that photolytically dissociate to methyl radicals and n-doped nanocrystals. Without oleic acid impurities, cadmium carboxylate can be completely displaced from the surface using n-alkylamines (NH2R', R' = n-butyl, n-hexyl, n-octyl) (≤0.01 carboxylates nm-2). Colloidal dispersions of amine bound nanocrystals (CdSe-NH2R') are indefinitely stable at amine concentrations of 0.1 M or higher and slowly aggregate at lower concentrations. Dissociation and evaporation of the amine ligands in 4-ethylpyridine, tri-n-butylphosphine, or molten tri-n-octylphosphine oxide solution results in nanocrystal aggregation. CdSe-NH2R' reacts with oleic acid, n-octadecylphosphonic acid, or carbon dioxide to form surface bound n-alkylammonium oleate, phosphonate, and carbamate ion pairs that bind with greater affinity than primary n-alkylamines. The results indicate that nanocrystal dispersions solely stabilized by neutral donor ligands are relatively unstable compared to those stabilized by adsorbed metal carboxylate or phosphonate complexes or by ion pairs. The challenge of differentiating between the neutral ligand bound form and adsorbed ion pairs is discussed.
authors.affiliation: Department of Chemistry, Columbia University , 3000 Broadway, MC 3121, New York, New York 10027, United States.
authors.forename: Peter E
authors.identifier: 0000-0001-6933-367X
authors.initials: PE
authors.lastname: Chen
authors.affiliation: Department of Chemistry, Columbia University , 3000 Broadway, MC 3121, New York, New York 10027, United States.
authors.forename: Nicholas C
authors.initials: NC
authors.lastname: Anderson
authors.affiliation: Department of Chemistry, Columbia University , 3000 Broadway, MC 3121, New York, New York 10027, United States.
authors.forename: Zachariah M
authors.initials: ZM
authors.lastname: Norman
authors.affiliation: Department of Chemistry, Columbia University , 3000 Broadway, MC 3121, New York, New York 10027, United States.
authors.forename: Jonathan S
authors.identifier: 0000-0001-5502-3267
authors.initials: JS
authors.lastname: Owen
mesh_terms: D000838:Anions / Q000737:chemistry; D001665:Binding Sites; D019187:Cadmium Compounds / Q000737:chemistry*; D002219:Carbamates / Q000737:chemistry*; D002264:Carboxylic Acids / Q000737:chemistry*; D015394:Molecular Structure; D053758:Nanoparticles / Q000737:chemistry*; D063065:Organophosphonates / Q000737:chemistry*; D018036:Selenium Compounds / Q000737:chemistry*
chemical_list: D000838:Anions; D019187:Cadmium Compounds; D002219:Carbamates; D002264:Carboxylic Acids; D063065:Organophosphonates; D018036:Selenium Compounds; C058667:cadmium selenide