Structural, electronic, and optical properties of the thiolate-protected Au38(SR)24 cluster are studied by density-functional theory computations (R = CH3 and R = C6H13) and by powder X-ray crystallography (R = C12H25). A low-energy structure which can be written as Au23at(Au(SR) 2)3(Au2(SR)3)6 having a biicosahedral core and a chiral arrangement of the protecting gold-thiolate Aux(SR)y units yields an excellent match between the computed (for R = C6H13) and measured (for R = C 12H25) powder X-ray diffraction function. We interpret in detail the electronic structure of the Au23 core by using a particle-in-a-cylinder model. Although the alkane thiolate ligands are achiral, the chiral structure of the ligand layer yields strong circular dichroism (CD) in the excitations below 2.2 eV for Au36(SCH3) 24. Our calculated CD spectrum is in quantitative agreement with the previously measured low-energy CD signal of glutathione-protected Au 38(SG)24. Our study demonstrates a new mechanism for the strong chiral response of thiolate-protected gold clusters with achiral metal cores and ligands.
ASJC Scopus subject areas
- Colloid and Surface Chemistry