Structure of Chiral Au44(2,4-DMBT)26 Nanocluster with an 18-Electron Shell Closure.

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 Au44(TBBT)28 (TBBTH = 4-tert-butylbenzenelthiol). The new cluster was determined to be Au44(2,4-DMBT)26 (2,4-DMBTH = 2,4-dimethylbenzenethiol) using multiple techniques, including mass spectrometry and single crystal X-ray crystallography (SCXC). Au44(2,4-DMBT)26 represents the first 18-electron closed-shell gold nanocluster. SCXC reveals that the atomic structure of Au44(2,4-DMBT)26 is completely different from that of Au44(TBBT)28 but is similar to the structure of Au38Q. The arrangement of staples (bridging thiolates) and part of the Au29 kernel atom induces the chirality of Au44(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 Au44(2,4-DMBT)26 bears an 18-electron shell closure structure, it is less thermostable than Au44(TBBT)28, indicating that multiple factors contribute to the thermostability of gold nanoclusters. Surprisingly, the small difference in Au/thiolate molar ratio between Au44(2,4-DMBT)26 and Au44(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 Au44(2,4-DMBT)26 is remarkably more positive than that in Au44(TBBT)28 and even slightly more positive than the charge states of gold in Au-(2,4-DMBT) or Au-TBBT complexes.