Ligand control in thiol stabilized Au-38 clusters

Alkyl thiols (CnH2n + 1SH) with chain lengths (n = 4, 6, 8, 12, 16) were investigated for etching the polydisperse Au-n(SG)(m) mixture in order to obtain nearly monodisperse Au-38(SR)(24) clusters. FT-IR studies demonstrate that all thiol ligands bound to Au-38 clusters are highly ordered and in an all-trans state. X-ray absorption studies at the S K-edge as well as at the Au L-3 edge show similarities between Au(I) S species and Au-38(SR)(24) clusters, in good agreement with the 'S-Au-S' capping motifs in the Au-38(SR)(24) structure and confirming charge transfer from gold to sulfur atoms. We report for the first time the use of Wide-angle X-ray scattering (WAXS) analysis as a more reliable tool than TEM to evaluate particle size and size distributions Au-38(SR)(24) clusters.