Electronic Structure and Photochemical Properties of a Monolayer-Protected Gold Cluster.

The electronic structure of a monolayer-protected gold cluster, [Au13(SCH3)8]3+, has been investigated by performing density functional calculations. The cluster has a characteristic structure with Oh molecular symmetry, and eight (111) facets of a centered cuboctahedral Au13 core cluster are fully passivated by eight methanethiolates. The bond distance between two neighboring gold atoms (3.673 Å) is much larger than that of the bare Au13 cluster (2.929 Å), whereas the Au-S bond distance is 2.403 Å. This atomic rearrangement means that the methanethiolates stabilize the enlarged bare Au13 cluster by bonding to the (111) hollow sites of the bare cluster. The absorption spectrum of the [Au13(SCH3)8]3+ cluster is simulated within time-dependent density functional theory. The spectrum shows clear absorption peaks and each peak is assigned to specific excitation processes. [ABSTRACT FROM AUTHOR]