Ligand Effects on the Structures of [Au₂₃L₆(C≡CPh)₉]²⁺ (L = N-Heterocyclic Carbene vs Phosphine) with Au₁₇ Superatomic Cores

Abstract

A n e w g o l d c l u s t e r c o m p o u n d [Au 23 (NHC ptol ) 6 (CCPh) 9 ] 2+ (NHC ptol = 1,3-di(paramethylbenzyl)benzimidazolin-2-ylidene) (Au 23 NHC ptol ) was synthesized, and its geometric and electronic structures were compared to those of a known phosphine-protected analogue [Au 23 (PPh 3 ) 6 (CCPh) 9 ] 2+ (Au 23 PPh 3 ). Single-crystal X-ray diffraction analysis revealed that Au 23 NHC ptol has a common structural motif with Au 23 PPh 3 : a Au 17 core capped by six NHC ligands and surrounded by three Au 2 (CCPh) 3 oligomers. However, a detailed inspection of the geometric structures elucidated two noticeable differences: (1) the Au 17 core of Au 23 NHC ptol is slightly elongated and sharpened along the C 3 axis compared with that of Au 23 PPh 3 and (2) all of the phenyl rings of the alkynyl ligands in Au 23 NHC ptol face nearly parallel to the equatorial plane of the Au 17 core, whereas randomly aligned phenyl rings are found in Au 23 PPh 3 . Both clusters showed comparable stability at 60 °C in chloroform. UV−vis absorption spectroscopy and differential pulse voltammetry indicated that both clusters exhibit similar electronic structures, but the highest occupied molecular orbital (HOMO) of Au 23 NHC ptol is higher in energy and the HOMO−lowest unoccupied molecular orbital (LUMO) gap of Au 23 NHC ptol is larger compared to Au 23 PPh 3 . Theoretical analysis of the electronic structures showed that the Au 17 core common to both clusters cannot be viewed as a dimer molecule composed of a prolate Au 10 (6e) superatom, but corresponds to a nonspherical superatom with 12 electrons.

N-Heterocyclic Carbene-Stabilized Hydrido Au24 Nanoclusters: Synthesis, Structure, and Electrocatalytic Reduction of CO2

“…Ligand-protected metal nanoclusters have emerged as an important class of nanomaterials with applications in bioimaging, optoelectronics, , and electrocatalysis. , Their atomically precise nature provides detailed insight into size–property relationships and an in-depth description of the bonding interaction between ligands and their metal core. , While thiol, , phosphine, and alkynyl-protected clusters have been widely explored, N-heterocyclic carbenes (NHCs) have been much less explored. , NHC-protected nanoclusters with metal core sizes Au 6 , Au 11 , Au 13 , and Au 25 have been reported, − and larger clusters were isolated by employing NHCs in combination with alkynyl (Au 23 ) and thiolate (Au 44 ) ligands. , NHC-protected clusters have been prepared with high stability and the ability to reduce CO 2 electrocatalytically …”

Insight Into the Stability and Electronic and Optical Properties of N-Heterocyclic Carbene Analogues of Halogen/Phosphine-Protected Au13Superatomic Clusters

“…Moreover, the recent incorporation of N-heterocyclic carbenes (NHC) as neutral ligands of gold AuNCs, as reported for the related [Au 13 (NHC) 9 Cl 3 ] 2+ cluster by Crudden and co-workers, and which displays a high emission quantum yield, allows us to further develop more versatile ligands owing to the central role of NHC ligands in organometallic chemistry. − Hence, their evaluation and comparison to phosphines may encourage further ligand engineering efforts and synthetic exploration of such species, − offering the opportunity of tuning nanocluster properties.…”

Synthesis and Characterization of Enantiopure Chiral Bis NHC-Stabilized Edge-Shared Au10 Nanocluster with Unique Prolate Shape

“…In 2019, our group reported the use of NHCs to protect gold nanoclusters, resulting in the first NHC-stabilized Au 11 and Au 13 nanoclusters. Later, the groups of Han, Zang, Mak, Tsukuda, and Zheng described successful syntheses of NHC-protected Au 11 , Au 13 , Au 23 , Au 25 , and Au 44 nanoclusters, illustrating the potential of NHCs as stabilizing ligands for gold nanoclusters.…”