Isomerization in Alkynyl-Protected Gold Nanoclusters

We report the controlled synthesis and structures of two isomeric gold nanoclusters, whose compositions are determined to be Au 23 (C≡CBu t ) 15 (denoted as Au 23 -1 and Au 23 -2 ) by single-crystal X-ray diffraction and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. This is the first time isomerism is discovered in alkynyl-protected gold nanoclusters. The metal-to-ligand ratios in these two clusters are different from known Au n (SR) m systems and have not been observed in the Au x (C≡CPh) y family. This pair of isomers exhibits different optical properties, although they have similar structures and identical components. For both Au 23 clusters, time-dependent density functional theory calculations revealed the frontier orbitals highest occupied molecular orbital (HOMO)–1, HOMO, and lowest unoccupied molecular orbital (LUMO) are mainly constructed from the Au 15 kernel and V-shaped alkynyl–gold motifs. The HOMO → LUMO transition of Au 23 -1 is optically forbidden, whereas it is allowed in Au 23 -2 . It is also found that Au 23 -2 cluster can be transformed to Au 23 -1 spontaneously under ambient conditions. This work offers further insight into the synthesis and isomerism of all-alkynyl-protected gold nanoclusters and will stimulate more investigation of isomeric metal nanoclusters.