Racemization of Chiral Pd₂Au₃₆(SC₂H₄Ph)₂₄: Doping Increases the Flexibility of the Cluster Surface

Pd₂Au₃₆(SC₂H₄Ph)₂₄ clusters have been prepared, isolated and separated in their enantiomers. Compared to the parent Au₃₈(SC₂H₄Ph)₂₄ cluster, the doping leads to a significant change of the circular dichroism spectrum; however, the anisotropy factors are of similar magnitude in both cases. Isolation of the enantiomers allowed us to study the racemization of the chiral cluster, which reflects the flexibility of the ligand shell composed of staple motifs. The doping leads to a substantial lowering of the racemization temperature. The change in activation parameters due to the doping may be solely due to modification of the electronic structure

Characterization of Cu–Zn/Core–Shell Al-MCM-41 as a Catalyst for Reduction of NO: Effect of Zn Promoter

A combination of three methodssubstitution, ion-exchange, and impregnationwas used to prepare the Cu–Zn/core–shell Al-MCM-41 catalyst with various copper species. The roles of each preparation method and of Zn promoter in the nature of copper were studied by means of in situ Fourier transform infrared spectroscopy of CO and NO adsorption, diffuse reflectance ultraviolet–visible–near-infrared spectroscopy, X-ray photoelectron spectroscopy, and H₂ temperature-programmed reduction. The results suggested that the different preparation methods strongly affected the nature of copper species. The amount of Cu­(I) species in reduced catalysts was promoted by the stabilization effect of Zn. In addition, Zn species also provide additional sites for the formation of nitrate and enhance the acidity of the catalysts

Structural Investigation of the Ligand Exchange Reaction with Rigid Dithiol on Doped (Pt, Pd) Au₂₅ Clusters

The ligand exchange reaction between heteroatom doped (Pd, Pt) Au₂₅(2-PET)₁₈ (2-PET = 2-phenylethylthiolate) clusters and enantiopure 1,1′-binaphthyl-2,2′-dithiol (BINAS) was monitored in situ using chiral high-performance liquid chromatography (HPLC). During the ligand exchange reactions, replacement of two protecting thiols (2-PET) with one new entering BINAS ligand on the cluster surface occurs. The rigid dithiol BINAS adsorbs in a specific mode that bridges the apex and one core site of two adjacent S­(R)–Au–S­(R)–Au–S­(R) units. This is the most favorable binding mode and theoretically preserves the original structure. A kinetic investigation on these in situ ligand exchange reactions revealed a decrease in reactivity after multiple exchange. A comparison of relative rate constants demonstrates a similar exchange rate toward BINAS for both (Pd, Pt) systems. The possible structural deformation after incorporation of BINAS was investigated by X-ray absorption spectroscopy (XAS) at the S K-edge and Au L₃-edge. First, a thorough assignment of all sulfur contributions to the XANES spectrum was performed, distinguishing for the first time long and short staple motifs. Following that, a structural comparison of doped systems using XANES and EXAFS confirmed the unaltered Au₂₅ structure, except for some slight influence on the Au–S bonds. Additionally, an intact staple motif was confirmed after incorporation of rigid dithiol BINAS by both XANES and EXAFS. This finding agrees with a BINAS interstaple binding mode predicted by calculation, which does not perturb the cluster structure

Directing Intrinsic Chirality in Gold Nanoclusters: Preferential Formation of Stable Enantiopure Clusters in High Yield and Experimentally Unveiling the “Super” Chirality of Au₁₄₄

Chiral gold nanoclusters offer significant potential for exploring chirality at a fundamental level and for exploiting their applications in sensing and catalysis. However, their widespread use is impeded by low yields in synthesis, tedious separation procedures of their enantiomeric forms, and limited thermal stability. In this study, we investigated the direct synthesis of enantiopure chiral nanoclusters using the chiral ligand 2-MeBuSH in the fabrication of Au25, Au38, and Au144 nanoclusters. Notably, this approach leads to the unexpected formation of intrinsically chiral clusters with high yields for chiral Au38 and Au144 nanoclusters. Experimental evaluation of chiral activity by circular dichroism (CD) spectroscopy corroborates previous theoretical calculations, highlighting the stronger CD signal exhibited by Au144 compared to Au38 or Au25. Furthermore, the formation of a single enantiomeric form is experimentally confirmed by comparing it with intrinsically chiral Au38(2-PET)24 (2-PET: 2-phenylethanethiol) and is supported theoretically for both Au38 and Au144. Moreover, the prepared chiral clusters show stability against diastereoisomerization, up to temperatures of 80 °C. Thus, our findings not only demonstrate the selective preparation of enantiopure, intrinsically chiral, and highly stable thiolate-protected Au nanoclusters through careful ligand design but also support the predicted “super” chirality in the Au144 cluster, encompassing hierarchical chirality in ligands, staple configuration, and core structure