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 Au₆₀S₆(SCH₂Ph)₃₆ by using electrospray ionization mass spectrometry and single crystal X-ray crystallography (SCXC). SCXC also reveals that Au₆₀S₆(SCH₂Ph)₃₆ consists of a fcc-like Au₂₀ kernel protected by a pair of giant Au₂₀S₃(SCH₂Ph)₁₈ staple motifs, which contain 6 tetrahedral-coordinate μ₄-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 Au₆₀S₆(SCH₂Ph)₃₆, is found in the crystals of Au₆₀S₆(SCH₂Ph)₃₆. 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.