title: The importance of nanocrystal precursor conversion kinetics: mechanism of the reaction between cadmium carboxylate and cadmium bis(diphenyldithiophosphinate).
abstract: We describe the synthesis of cadmium bis(diphenyldithiophosphinate) (Cd(S(2)PPh(2))(2)) from secondary phosphine sulfides and its conversion to cadmium sulfide nanocrystals. Heating Cd(S(2)PPh(2))(2) and cadmium tetradecanoate (≥4 equiv) to 240 °C results in complete conversion of Cd(S(2)PPh(2))(2) to cadmium sulfide nanocrystals with tetradecanoate surface termination. The nanocrystals have a narrow size distribution (d = 3.8-4.1 nm, σ < 10%) that is evident from the line width of the lowest energy absorption feature (λ = 412-422 nm, fwhm = 0.17 eV) and display bright photoluminescence (PLQY(band edge+trap) = 36%). Interestingly, the final diameter is insensitive to the reaction conditions, including the total concentration of precursors and initial cadmium to sulfur ratio. Monitoring the reaction with (31)P NMR, UV-visible, and infrared absorption spectroscopies shows that the production of cadmium diphenylphosphinate (Cd(O(2)PPh(2))(2)) and tetradecanoic anhydride co-products is coupled with the formation of cadmium sulfide. From these measurements we propose a balanced chemical equation for the conversion reaction and use it to optimize a synthesis that affords CdS nanocrystals in quantitative yield. In light of these results we discuss the importance of well-defined precursor reactivity to reproducible conversion kinetics and the synthesis of nanocrystals with unambiguous chemical composition.
authors.affiliation: Department of Chemistry, Columbia University, New York, New York 10027, United States.
authors.forename: Mark P
authors.initials: MP
authors.lastname: Hendricks
authors.forename: Brandi M
authors.initials: BM
authors.lastname: Cossairt
authors.forename: Jonathan S
authors.initials: JS
authors.lastname: Owen
mesh_terms: D019187:Cadmium Compounds / Q000737:chemistry*; D003460:Crystallization / Q000379:methods*; D046911:Macromolecular Substances / Q000737:chemistry; D008422:Materials Testing; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D010720:Phosphines / Q000737:chemistry*; D013440:Sulfides / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D019187:Cadmium Compounds; D046911:Macromolecular Substances; D010720:Phosphines; D013440:Sulfides; C034939:cadmium sulfide