On the Dynamic Stoichiometry of Metal Chalcogenide Nanocrystals: Spectroscopic Studies of Metal Carboxylate Binding and Displacement

By N. Anderson, M. Hendricks, Joshua J. Choi, J. Owen. Journal of the American Chemical Society, 2013

783 citations recorded by the source corpus.

We demonstrate that metal carboxylate complexes (L–M(O2CR)2, R = oleyl, tetradecyl, M = Cd, Pb) are readily displaced from carboxylate-terminated ME nanocrystals (ME = CdSe, CdS, PbSe, PbS) by various Lewis bases (L = tri-n-butylamine, tetrahydrofuran, tetradecanol, N,N-dimethyl-n-butylamine, tri-n-butylphosphine, N,N,N',N'-tetramethylbutylene-1,4-diamine, pyridine, N,N,N',N'-tetramethylethylene-1,2-diamine, n-octylamine). The relative displacement potency is measured by 1H NMR spectroscopy and depends most strongly on geometric factors like sterics and chelation, though also on the hard/soft match with the cadmium ion. The results suggest that ligands displace L–M(O2CR)2 by cooperatively complexing the displaced metal ion as well as the nanocrystal. Removal of up to 90% of surface bound Cd(O2CR)2 from CdSe and CdS nanocrystals decreases the Cd:Se ratio from 1.1 ± 0.06 to 1.0 ± 0.05, broadens the 1Se-2S3/2h absorption and decreases the photoluminescence quantum yield (PLQY) from 10% to <1% (CdSe) and 20% to <1% (CdS). These changes are partially reversed upon rebinding of M(O2CR)2 at room temperature (~60 %) and fully reversed at elevated temperature. A model is proposed where electron accepting M(O2CR)2 complexes (Z-type ligands) reversibly bind to nanocrystals leading to a range of stoichiometries for a given core size. The results demonstrate that nanocrystals lack a single chemical formula, but are instead dynamic structures with concentration-dependent compositions. The importance of these findings to the synthesis and purification of nanocrystals as well as ligand exchange reactions is discussed.

Subfields: Electrical and Electronic Engineering, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/5839489a0be674580411443fb9c409a032aaf0fe

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Citations in the corpus

Prospects of nanoscience with nanocrystals. (2015, positive): “217 This enables NCs with a wide range of surface terminations and M:E stoichiometries to be purposely formed, and it explains why, for example, exposure to amines has been deemed e ﬀ ective to remove X-type ligands from PbS or PbSe NCs. 218 The intrinsically di ﬀ erent surface chemistry related to…”
Highly Dynamic Ligand Binding and Light Absorption Coefficient of Cesium Lead Bromide Perovskite Nanocrystals. (2016, background): “Such observations were already explained in earlier work, the broad resonance was assigned to tightly bound ligands, in slow exchange with weakly bound ligands, featuring sharp resonances.(24,27,29) Indeed, in the DOSY experiment we observed a slowly diffusing component with D = 59± 9 μm(2)/s.”
Building devices from colloidal quantum dots (2016, background): “The interactions between the QD core and ligand head-group can be rationalized by using the concepts originally developed for molecular coordination compounds and recently adapted to NC surfaces (24, 25).”