Crystalline Superlattices of Nanoscopic CdS Molecular Clusters: An X-ray Crystallography and¹¹¹Cd SSNMR Spectroscopy Study

Abstract

Systematic Cd solid-state (SS) NMR experiments were performed to correlate X-ray crystallographic data with SSNMR parameters for a set of CdS-based materials, varying from molecular crystals of small complexes [Cd(SPh)] and [Cd(SPh)] to superlattices of large monodisperse clusters [CdS(SPh)(dmf)] and 1.9 nm CdS. Methodical data analysis allowed for assigning individual resonances or resonance groups to particular types of cadmium sites residing in different chemical and/or crystallographic environments. For large CdS frameworks, Cd resonances were found to form three groups. This result is noteworthy, since for related systems with size polydispersity and variations in composition, such as CdS or CdSe nanoparticles protected with an organic ligand shell, typically only two groups of resonances were observed. The generalized information obtained in this work can be used for the interpretation ofCd SSNMR data for large CdS clusters and nanoparticles, for which crystal structure analysis remains inaccessible. Comparison of the powder X-ray diffraction patterns for freshly prepared and dried superlattices of large CdS clusters revealed an interesting superstructure rearrangement that was not observed for the smaller frameworks.

Probing the Surface Structure of Semiconductor Nanoparticles by DNP SENS with Dielectric Support Materials

“…Most of the elements found in main group inorganic semiconductors have NMR active nuclei, potentially making solid-state NMR an ideal tool for probing the structure of NPs. Solid-state NMR has previously been applied to a number of different NP systems, such as cadmium chalcogenides (CdX, X = S, Se, Te), [26][27][28][29][30][31][32][33][34] indium phosphide (InP), [35][36][37] silicon (Si), [38][39][40][41][42] etc., [43][44][45][46] to determine both the surface and bulk structure. Direct excitation solid-state NMR experiments mainly probe the bulk of the NPs, although surface NMR signals are visible in small diameter NP NMR spectra.…”

“…Most of the elements found in main-group inorganic semiconductors have NMR-active nuclei, potentially making solid-state NMR an ideal tool for probing the structure of NPs. Solid-state NMR has previously been applied to a number of different NP systems, such as cadmium chalcogenides (CdX, X = S, Se, Te), − indium phosphide (InP), − silicon (Si), − etc., − to determine both the surface and bulk structure. Direct excitation solid-state NMR experiments mainly probe the bulk of the NPs, although surface NMR signals are visible in the NMR spectra of small-diameter NP. ,,,,, The chemical shift of the core NMR signals is often correlated to the band gap and particle size of semiconductor NPs. ,,,,, Solid-state NMR can also selectively probe the surface of inorganic NPs.…”

113Cd Solid-State NMR at 21.1 T Reveals the Local Structure and Passivation Mechanism of Cadmium in Hybrid and All-Inorganic Halide Perovskites

“…Cadmium-113 (spin I = 1/2, 12.2% abundant) has a receptivity 8 times higher than that of 13 C and has been widely used to experimentally and theoretically study inorganic compounds, molecular complexes, − nanoparticles, − MOFs, and metal ion binding sites in proteins. , Cadmium-111 (spin I = 1/2, 12.8% abundant) has similar receptivity to that of cadmium-113 and is occasionally used as an alternative, yielding identical structural information . Cadmium-113 typically exhibits chemical shift anisotropy on the order of 10–300 ppm in inorganic cadmium compounds and up to 600 ppm in coordination complexes, which is substantially reduced by magic angle spinning (MAS) at moderate spin rates (∼20 kHz).…”

“…44,45 Cadmium-111 (spin I = 1/2, 12.8% abundant) has similar receptivity to that of cadmium-113 and is occasionally used as an alternative, yielding identical structural information. 46 Cadmium-113 typically exhibits chemical shift anisotropy on the order of 10−300 ppm in inorganic cadmium compounds 35 and up to 600 ppm in coordination complexes, 47 which is substantially reduced by magic angle spinning (MAS) at moderate spin rates (∼20 kHz).…”

Core-Doped [(Cd1–xCox)10S4(SPh)16]4– Clusters from a Self-Assembly Route

“…Inorganic semiconductor nanoclusters have gained interest for their atomically precise sizes and well-defined structures. , The class of molecular metal chalcogenide clusters can range in size from tens to hundreds of atoms within the core and up to ∼2 nm in size. These clusters experience size-dependent changes in their electronic structures, including the observations that larger nanoclusters have some overlapping properties with colloidal nanocrystals. − These similarities make nanocluster molecules ideal structural and spectroscopic analogues to larger nanocrystals. , Developing synthetic methods for achieving a diverse range of cluster sizes has been challenging. Some previously synthesized examples of these molecular clusters of particular interest are the cadmium thiophenolate species including [Cd­(SPh) 4 ] 2– (Cd 1 ), [Cd 4 (SPh) 10 ] 2– (Cd 4 ), [Cd 10 S 4 (SPh) 16 ] 4– (Cd 10 ), [Cd 8 S­(SPh) 16 ] 2– (Cd 8 ), [Cd 17 S 4 (SPh) 28 ] 2– (Cd 17 ), and [Cd 32 S 14 (SPh) 36 (dmf) 4 ] (Cd 32 ). − Additionally, there have been many reports on the role of cluster species within the growth mechanism of quantum dots (QDs), in addition to the use of molecular clusters as precursors for further growth. − The use of molecular cluster precursors has also been promising for effectively doping QDs with transition metal ions. , With increasing evidence of clusters being metastable intermediates in the synthesis of colloidal semiconductor nanocrystals, the attention of many researchers has shifted to understanding the chemistry of these cluster species and related magic-size nanocrystals as they may be critical to controlling dopant distributions within nanocrystals and maintaining narrow size distributions. − …”