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

Two homoleptic alkynyl-protected gold clusters with compositions of Na[Au25 (C≡CAr)18 ] and (Ph4 P)[Au25 (C≡CAr)18 ] (Na⋅1 and Ph4 P⋅1, Ar=3,5-bis(trifluoromethyl)phenyl) were synthesized via a direct reduction method. 1 is a magic cluster analogous to [Au25 (SR)18 ]- in terms of electron counts and metal-to-ligand ratio. Single-crystal structure analysis reveals that 1 has an identical Au13 kernel to [Au25 (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 D3 arrangement of Au25 . 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.