Critical sizes in the growth of Au clusters

A systematic exploration of the growth of Au clusters has revealed a critical size for the formation of stable assemblies. Mass-spectrometric measurements of clusters, as grown in the presence of an excess of weakly binding long-chain n-alkylthiol(ate) groups, show high yields of new compounds with core masses near the 15k minimum (approximate to 75 Au atoms; k = 10(3) amu), and also at 23k, and 29k. Structural analyses establish their cores as compact metal nanocrystals of the corresponding effective diameters (1.4 to 1.7 nm), probably of decahedral close-packing and morphology. The precise identities of this sequence of special structures can now be sought.