Same Magic Number but Different Arrangement: Alkynyl-Protected Au25 with D3 Symmetry

Two homoleptic alkynyl-protected gold clusters with compositions of Na[Au-25(CCAr)(18)] and (Ph4P)[Au-25(CCAr)(18)] (Na.1 and Ph4P.1, Ar=3,5-bis(trifluoromethyl)phenyl) were synthesized via a direct reduction method. 1 is a magic cluster analogous to [Au-25(SR)(18)](-) in terms of electron counts and metal-to-ligand ratio. Single-crystal structure analysis reveals that 1 has an identical Au-13 kernel to [Au-25(SR)(18)](-), but adopts a distinctly different arrangement of the six peripheral dimer staple motifs. The steric hindrance of alkynyl ligands is responsible for the D-3 arrangement of Au-25. The introduction of alkynyl also significantly changes the optical absorption features of the nanocluster as supported by DFT calculations. This magic cluster confirms that there is a similar but quite different parallel alkynyl-protected metal cluster universe in comparison to the thiolated one.