The structure of the Au₁₅–thiolate cluster has been elucidated using a DFT approach, and it is demonstrated to comprise a Au₄–tetrahedron core protected solely by the combination of two concatenated staple motifs. The longer motif efficiently wraps the core, and threads the shorter one. The structural assignment is supported by comparison to the powder X-ray diffraction pattern and, via time dependent-DFT calculations, to the optical and chiroptical (CD) absorption spectra. The calculated CD spectrum features a characteristic strong peak centered at 3.48 eV in accordance with the experimental profile. These results confirm the existence of long Au(I)–thiolate motifs as protecting units of small thiolated gold clusters with a thiolate-to-gold ratio comparable to the Au₁₅(SR)₁₃ cluster.

The structure and optical properties of a set of R-1,1′-binaphthyl-2,2′-dithiol (R-BINAS) monosubstituted A-Au₃₈(SCH₃)₂₄ clusters are studied by means of time dependent density functional theory (TD-DFT). While it was proposed earlier that BINAS selectively binds to monomer motifs (SR-Au-SR) covering the Au₂₃ core, our calculations suggest a binding mode that bridges two dimer (SR-Au-SR-Au-RS) motifs. The more stable isomers show a negligible distortion induced by BINAS adsorption on the Au₃₈(SCH₃)₂₄ cluster which is reflected by similar optical and Circular Dichroism (CD) spectra to those found for the parent cluster. The results furthermore show that BINAS adsorption does not enhance the CD signals of the Au₃₈(SCH₃)₂₄ cluster.