Atomistic Description of Thiostannate-Capped CdSe Nanocrystals: Retention of Four-Coordinate SnS4 Motif and Preservation of Cd-Rich Stoichiometry

Abstract

Colloidal semiconductor nanocrystals (NCs) are widely studied as building blocks for novel solid-state materials. Inorganic surface functionalization, used to displace native organic capping ligands from NC surfaces, has been a major enabler of electronic solid-state devices based on colloidal NCs. At the same time, very little is known about the atomistic details of the organic-to-inorganic ligand exchange and binding motifs at the NC surface, severely limiting further progress in designing all-inorganic NCs and NC solids. Taking thiostannates (K4SnS4, K4Sn2S6, K6Sn2S7) as typical examples of chalcogenidometallate ligands and oleate-capped CdSe NCs as a model NC system, in this study we address these questions through the combined application of solution 1H NMR spectroscopy, solution and solid-state 119Sn NMR spectroscopy, far-infrared and X-ray absorption spectroscopies, elemental analysis, and by DFT modeling. We show that through the X-type oleate-to-thiostannate ligand exchange, CdSe NCs retain their Cd-rich stoichiometry, with a stoichiometric CdSe core and surface Cd adatoms serving as binding sites for terminal S atoms of the thiostannates ligands, leading to all-inorganic (CdSe)core[Cdm(Sn2S7)yK(6y-2m)]shell (taking Sn2S76– ligand as an example). Thiostannates SnS44– and Sn2S76– retain (distorted) tetrahedral SnS4 geometry upon binding to NC surface. At the same time, experiments and simulations point to lower stability of Sn2S64– (and SnS32–) in most solvents and its lower adaptability to the NC surface caused by rigid Sn2S2 rings.

Crystal Structures and Selected Properties of CoII Containing Thiostannates prepared by a New Room Temperature Route

“…As can be seen in Figure only one signal is observed and no significant changes occurred during six days. The chemical shift of 55 ppm matches well with literature values for the [Sn 2 S 6 ] 4– anion . To prevent formation of Co 2+ centered aqua complexes, the Co 2+ cation must be complexed by e.g.…”

Rare Earth Chalcogels NaLnSnS4 (Ln = Y, Gd, Tb) for Selective Adsorption of Volatile Hydrocarbons and Gases

“…Raman investigations were carried out to confirm the presence of [SnS 4 ] 4– anions within the chalcogel structures. Raman bands at 347–317 cm –1 and 368 cm –1 (Figure S12, Supporting Information), characteristic of symmetric and asymmetric Sn–S modes of [SnS 4 ] 4– , are observed . The results confirm that the building blocks remained intact within the chalcogels.…”

Spectroelectrochemical Signatures of Surface Trap Passivation on CdTe Nanocrystals

“…This is in agreement with the observation that NCs are often metal rich, where negative X-type ligands (e.g., carboxylates) 16 compensate for the excess positive charge of the metal cations. 10 , 17 , 24 , 48 , 49 …”