The Influence of Flexibility of Alkynyl Ligands on the Formation of an Fcc Au Nanocluster.

Isomerization of nanoclusters is helpful for understanding the relationships between structures and properties. Surface-protecting ligands play a crucial role in controlling the atomic packing mode of the inner core. The synthesis and total structural determination of the all alkynyl-protected gold nanocluster (NEtCHCl)[Au(C≡CCHPh)] (Au-1) are reported. Au-1 and the previously reported [Au(C≡CCH-4-CF)] (Au-2) constitute the largest alkynyl-protected nanocluster quasi-isomers (> 100 metal atoms). Both Au consist of an fcc Au kernel and a shell of 24 RC≡C─Au─C≡CR staples, but the specific arrangements are different. The application of the flexible alkynyl ligands creates a significant difference in the face-centered cubic (fcc) kernel structure in Au-1, showing a different electronic structure, thermal- and photo-stability. Transient absorption spectra reveal that Au-1 still does not show any metallic characteristics, even though it has a smaller energy gap (Eg) than Au-2.