On the structure of the Au-18(SR)(14) cluster

First principles calculations are used for a systematic search of the lowest-energy (most-stable) structure of the recently synthesized Au-18(SR)(14) cluster. A comparison of the calculated optical absorption and electronic circular dichroism spectra, which are highly sensitive to the cluster structure and chirality, with the experimental spectra of the glutathione-protected gold cluster, Au-18(SG)(14), is used to discriminate between low-energy isomers of the Au-18(SR)(14) (R = CH3) cluster. From the good agreement between calculated and measured spectra, it is predicted that the structure of the Au-18(SR)(14) cluster consists of a prolate Au-8 core covered with two dimer (SR-Au-SR-Au-SR) and two trimer (SR-Au-SR-Au-SR-Au-SR) motifs. These results provide additional evidence on the existence of longer trimer motifs as protecting units of small thiolated gold clusters.