Alkynyl-protected Au23 nanocluster: a 12-electron system.

A 23-gold-atom nanocluster was prepared by NaBH4-mediated reduction of a solution of PhC≡CAu and Ph3PAuSbF6 in CH2Cl2. The cluster composition was determined to be [Au23(PhC≡C)9(Ph3P)6](2+) and single-crystal X-ray diffraction revealed that the cluster has an unprecedented Au17 kernel protected by three PhC2-Au-C2 (Ph)-Au-C2 Ph motifs and six Ph3P groups. The Au17 core can be viewed as the fusion of two Au10 units sharing a Au3 triangle. Electronic structure analysis from DFT calculations suggests that the stability of this unusual 12-electron cluster is a result of the splitting of the superatomic 1D orbitals under D3h symmetry of the Au17 kernel. The discovery and determination of the structure of the Au23 cluster demonstrates the versatility of the alkynyl ligand in leading to the formation of new cluster compounds.