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Au 40 (SR) 24 Cluster as a Chiral Dimer of 8-Electron Superatoms: Structure and Optical Properties

2012; American Chemical Society; Volume: 134; Issue: 48 Linguagem: Inglês

10.1021/ja309619n

1943-2984

Sami Malola, Lauri Lehtovaara, Stefan Knoppe, Kuo‐Juei Hu, Richard E. Palmer, Thomas Bürgi, Hannu Häkkinen,

Pharmacological Effects and Toxicity Studies

We predict and analyze density-functional theory (DFT)-based structures for the recently isolated Au(40)(SR)(24) cluster. Combining structural information extracted from ligand-exchange reactions, circular dichroism and transmission electron microscopy leads us to propose two families of low-energy structures that have a chiral Au-S framework on the surface. These families have a common geometrical motif where a nonchiral Au(26) bi-icosahedral cluster core is protected by 6 RS-Au-SR and 4 RS-Au-SR-Au-SR oligomeric units, analogously to the "Divide and Protect" motif of known clusters Au(25)(SR)(18)(-/0), Au(38)(SR)(24) and Au(102)(SR)(44). The strongly prolate shape of the proposed Au(26) core is supported by transmission electron microscopy. Density-of-state-analysis shows that the electronic structure of Au(40)(SR)(24) can be interpreted in terms of a dimer of two 8-electron superatoms, where the 8 shell electrons are localized at the two icosahedral halves of the metal core. The calculated optical and chiroptical characteristics of the optimal chiral structure are in a fair agreement with the reported data for Au(40)(SR)(24).