Electronic Structure and Optical Properties of the Thiolate-Protected Au28(SMe)20 Cluster

The recently reported crystal structure of the Au-28(TBBT)(20) cluster (TBBT: p-tert-butylbenzenethiolate) is analyzed with (time-dependent) density functional theory (TD-DFT). Bader charge analysis reveals a novel trimeric Au-3(SR)(4) binding motif. The cluster can be formulated as Au-14(Au-2(SR)(3))(4)(Au-3(SR)(4))(2). The electronic structure of the Au-14(6+) core and the ligancl-protected cluster were analyzed, and their stability can be explained by formation of distorted eight-electron superatoms. Optical absorption and circular dichroism (CD) spectra were calculated and compared to the experiment. Assignment of handedness of the intrinsically chiral cluster is possible.