Isomerization in Alkynyl-Protected Gold Nanoclusters

We report the controlled synthesis and total structure of two isomeric gold nanoclusters, whose compositions were determined to be Au23(C≡CBut)15 (denoted as Au23-1 and Au23-2) by single-crystal X-ray diffraction and matrix-assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-TOF-MS). This is the first time to discover isomerism in alkynyl-protected gold nanoclusters. The metal-to-ligand ratios in these two clusters are different from known Aun(SR)m systems and have not been observed among Aux(C≡CPh)y family. This pair isomers exhibit different optical properties, although they have similar structures and identical components. For both Au23, TDDFT calculations revealed the frontier orbitals HOMO-1, HOMO, LUMO are mainly contributed from Au15 kernel and V-shaped alkynyl-gold motifs. The HOMO→LUMO transition of Au23-1 is optically forbidden, while it is allowed in Au23-2. It is also found that Au23-2 cluster can be transformed to Au23-1 spontaneously under ambient conditions. This wo...