The fourth crystallographic closest packing unveiled in the gold nanocluster crystal.

Metal nanoclusters have recently attracted extensive interest not only for fundamental scientific research, but also for practical applications. For fundamental scientific research, it is of major importance to explore the internal structure and crystallographic arrangement. Herein, we synthesize a gold nanocluster whose composition is determined to be AuS(SCHPh) by using electrospray ionization mass spectrometry and single crystal X-ray crystallography (SCXC). SCXC also reveals that AuS(SCHPh) consists of a fcc-like Au kernel protected by a pair of giant AuS(SCHPh) staple motifs, which contain 6 tetrahedral-coordinate μ-S atoms not previously reported in the Au-S interface. Importantly, the fourth crystallographic closest-packed pattern, termed 6H left-handed helical (6HLH) arrangement, which results in the distinct loss of solid photoluminescence of amorphous AuS(SCHPh), is found in the crystals of AuS(SCHPh). The solvent-polarity-dependent solution photoluminescence is also demonstrated. Overall, this work provides important insights about the structure, Au-S bonding and solid photoluminescence of gold nanoclusters.