Ligand Addition Energies and the Stoichiometry of Colloidal Nanocrystals

Abstract

Experimental nonstoichiometries of colloidal nanocrystals such as CdSe and PbS are accounted for by attributing to each constituent atom and capping ligand a formal charge equal to its most common oxidation state to obtain an overall neutral nanocrystal. In spite of its apparent simplicity, little theoretical support of this approach-called here the oxidation-number sum rule-is present in the current literature. Here, we introduce the ligand addition energy, which we define as the energy gained or expended upon the transfer of one ligand from a reference state to a metal-rich solid surface. For the combination of CdSe, ZnSe and InP with either chalcogen, halogen or hydrochalcogen ligands, we compute successive ligand addition energies using ab initio methods and determine the thermodynamically stable surface composition as that composition where ligand addition turns endothermic. We find that the oxidation-number sum rule is valid in many situations, although exceptions occur for each material studied, most notably when exposed to small oxidative ligands. In the case of InP, however, violations are more severe, extending toward the entire chalcogen ligand family. In addition, we find that electronegativity rather than chemical hardness is a reasonable predictor for ligand addition energies, with the most electronegative ligands yielding the most exothermic addition energies. Finally, we argue that the ligand addition energy will be a most useful quantity for future computational studies on the structure, stability and reactivity of nanocrystal surfaces.

Safe‐by‐Design Ligand‐Coated ZnO Nanocrystals Engineered by an Organometallic Approach: Unique Physicochemical Properties and Low Toxicity toward Lung Cells

“…In addition, we used the TGA data to estimate the graftingd ensity of the organic ligands in ZnO-MEAA NCs (for details, see the Supporting Information). [25,26] The average hydrodynamic diametero ft he ZnO-MEAA NCs was about 12 nm in both THF and DMSO solutions( Figure S4 in the Supporting Information). [24] These observations indicate that our organometallicw et-chemical method provides ZnO NCs of the generic chemical formula [(ZnO) x {Zn(MEAA) 2 } y (MEAA) z ], [25] that is, ZnO NCs with ac omplex nanocrystal/ligand interface likely incorporating MEAA,Z n(MEAA) 2 ,a nd oxozinc species stabilized by the carboxylate ligands.…”

Covalent Functionalization of Nickel Phosphide Nanocrystals with Aryl-Diazonium Salts

“…62,63 Well understood mechanisms for ligand exchange have been developed based on concentration gradients, salt metathesis, and displacement by higher binding affinity head groups. [64][65][66][67][68][69][70] Unfortunately, the same chemical principles that make these ligand exchange reactions viable also make them unstable in catalytically relevant conditions. Especially the strong acid conditions, typically 0.5 M sulfuric acid, required for HER lead to the protonation and desorption of such ligands.…”

Functionalisation of Colloidal Transition Metal Sulphides Nanocrystals: A Fascinating and Challenging Playground for the Chemist

“…Its intrinsic luminescence and the possibility of easy doping disclose its application in optoelectronics and related fields [8]. Moreover, it is environmental friendly and not-cytotoxic [298,299], thus suggesting possible applications also in biomedicine. In fact, combining the biocompatibility and the luminescence, optical bioimaging applications can be pursued [298,299].…”

“…Likewise, they can be diamagnetic, paramagnetic, ferromagnetic or antiferromagnetic [1,44,[293][294][295][296]. A relevant functional property displayed by some metal sulphides, particularly upon doping, is luminescence [46], which is broadly used also in optical bioimaging applications of these compounds [1,10,44,[297][298][299][300]. Sulphide-based luminescent materials have attracted much attention for a wide range of photo-, cathodo-and electroluminescent applications.…”

“…Moreover, it is environmental friendly and not-cytotoxic [298,299], thus suggesting possible applications also in biomedicine. In fact, combining the biocompatibility and the luminescence, optical bioimaging applications can be pursued [298,299]. For all these reasons and thanks to ZnS non-toxicity and intrinsic photoluminescence, ZnS NPs can be envisioned as high-performance and biocompatible bioimaging probes, although their stable dispersion in aqueous media still remains an open challenge, as discussed in the following.…”