Nan Yan

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.

Transition-sized Au92 nanoparticle bridging non-fcc-structured gold nanoclusters and fcc-structured gold nanocrystals

Herein, we report the intriguing structure, optical absorption and electrochemical properties of the transition-sized Au92(TBBT)44 (Au92 for short, TBBT = 4-tert-butylbenzenethiolate) nanoparticle. An interesting observation is the 4H phase array of Au92 nanoparticles in the unit cells of single crystals.

Unraveling the long-pursued Au144 structure by x-ray crystallography

A mysterious, long-pursued structure of a nanocluster-nanocrystal transition-sized nanoparticle is unraveled. The transition from nanocluster to nanocrystal is a central issue in nanoscience. The atomic structure determination of metal nanoparticles in the transition size range is challenging and particularly important in understanding the quantum size effect at the atomic level. On the basis of the rationale that the intra- and interparticle weak interactions play critical roles in growing high-quality single crystals of metal nanoparticles, we have reproducibly obtained ideal crystals of Au144(SR)60 and successfully solved its structure by x-ray crystallography (XRC); this structure was theoretically predicted a decade ago and has long been pursued experimentally but without success until now. Here, XRC reveals an interesting Au12 hollow icosahedron in thiolated gold nanoclusters for the first time. The Au–Au bond length, close to that of bulk gold, shows better thermal extensibility than the other Au–Au bond lengths in Au144(SR)60, providing an atomic-level perspective because metal generally shows better thermal extensibility than nonmetal materials. Thus, our work not only reveals the mysterious, long experimentally pursued structure of a transition-sized nanoparticle but also has important implications for the growth of high-quality, single-crystal nanoparticles, as well as for the understanding of the thermal extensibility of metals from the perspective of chemical bonding.