Structure of Chiral Au_(44)(2,4-DMBT)_(26) Nanocluster with an 18-Electron Shell Closure

摘要

The 18-electron shell closure structure of Au nanoclusters protected by thiol ligands has not been reported until now. Herein, we synthesize a novel nanocluster bearing the same gold atom number but a different thiolate number as another structurally resolved nanocluster Au_(44)(TBBT)_(28) (TBBTH = 4-tert-butylbenze-nelthiol). The new cluster was determined to be Au_(44)(2,4-DMBT)_(26) (2,4-DMBTH = 2,4-dimethylbenzenethiol) using multiple techniques, including mass spectrometry and single crystal X-ray crystallography (SCXC). Au_(44)(2,4-DMBT)_(26) represents the first 18-electron closed-shell gold nanocluster. SCXC reveals that the atomic structure of Au_(44)(2,4-DMBT)_(26) is completely different from that of Au_(44)(TBBT)_(28) but is similar to the structure of Au_(38Q). The arrangement of staples (bridging thiolates) and part of the Au_(29) kernel atom induces the chirality of Au_(44)(2,4-DMBT)_(26). The finding that a small portion of the gold kernel exhibits chirality is interesting because it has not been previously reported to the best of our knowledge. Although Au_(44)(2,4-DMBT)_(26) bears an 18-electron shell closure structure, it is less thermostable than Au_(44)(TBBT)_(28), indicating that multiple factors contribute to the thermostability of gold nanodusters. Surprisingly, the small difference in Au/thiolate molar ratio between Au_(44)(2,4-DMBT)_(26) and Au_(44)(TBBT)_(28) leads to a dramatic distinction in Au 4f X-ray photoelectron spectroscopy, where it is found that the charge state of Au in Au_(44)(2,4-DMBT)_(26) is remarkably more positive than that in Au_(44)(TBBT)_(28) and even slightly more positive than the charge states of gold in Au-(2,4-DMBT) or Au-TBBT complexes.