ABSTRACT
Reported herein are the synthesis and structures of two high-nuclearity AuAg nanoclusters, namely, [Au78Ag66(C≡CPh)48Cl8]q- and [Au74Ag60(C≡CPh)40Br12]2-. Both clusters possess a three-concentric-shell Au12@Au42@Ag60 structure. However, the dispositions of the metal atoms, and the ligand coordination modes, of the outermost shells of these clusters are distinctly different. These structural differences reflect the bonding characteristics of the halide ligands. As revealed by density functional theory analysis, these clusters exhibit superatomic electron shell closings at magic numbers of 92 (for q = 4) and 84, respectively, consistent with their spherical shapes. Both clusters exhibit unusual multivalent redox properties.
ABSTRACT
No formation of bulk silver hydride has been reported. Until very recently, only a few silver nanoclusters containing hydrides have been successfully prepared. However, due to the lack of effective techniques and also poor stability of hydride-containing Ag nanoclusters, the identification of hydrides' location within Ag nanoclusters is challenging and not yet achieved, although some successes have been reported on clusters of several Ag atoms. In this work, we report a detailed structural and spectroscopic characterization of the [Ag40(DMBT)24(PPh3)8H12]2+ (Ag40H12) cluster (DMBT = 2,4-dimethylbenzenethiol). The metal framework consists of three concentric shells of Ag8@Ag24@Ag8, which can be described as (ν1-cube)@(truncated-ν3-octahedron)@(ν2-cube), respectively. The presence of 12 hydrides in each cluster was systematically identified by various techniques. Based on a detailed analysis of the structural features and 1H and 2H NMR spectra, the positions of the 12 hydrides were determined to be residing on the 12 edges of the cubic core. As a result, the electron count of the Ag40 cluster is a two-electron superatomic system instead of a 14-electron system. Moreover, based on our DFT calculations and experimental probes, it was demonstrated that the 12 hydrides play a crucial role in stabilizing both the electronic and geometric structure of the Ag40H12 cluster. The successful synthesis of stable hydride-containing Ag nanoclusters and the identification of hydride positions are expected to simulate research attention on both synthesis and application of hydride-containing Ag nanomaterials.
ABSTRACT
A general method, using mixed ligands (here diphosphines and thiolates) is devised to turn an achiral metal cluster, Au13 Cu2 , into an enantiomeric pair by breaking (lowering) the overall molecular symmetry with the ligands. Using an achiral diphosphine, a racemic [Au13 Cu2 (DPPP)3 (SPy)6 ]+ was prepared which crystallizes in centrosymmetric space groups. Using chiral diphosphines, enantioselective synthesis of an optically pure, enantiomeric pair of [Au13 Cu2 ((2r,4r)/(2s,4s)-BDPP)3 (SPy)6 ]+ was achieved in one pot. Their circular dichroism (CD) spectra give perfect mirror images in the range of 250-500â nm with maximum anisotropy factors of 1.2×10-3 . DFT calculations provided good correlations with the observed CD spectra of the enantiomers and, more importantly, revealed the origin of the chirality. Racemization studies show high stability (no racemization at 70 °C) of these chiral nanoclusters, which hold great promise in applications such as asymmetry catalysis.
