Chiral Structure of Thiolate-Protected 28-Gold-Atom Nanocluster Determined by X‑ray Crystallography

We
report the crystal structure of a new nanocluster formulated
as Au28(TBBT)20, where TBBT = 4-tert-butylbenzenethiolate. It exhibits a rod-like Au20 kernel
consisting of two interpenetrating cuboctahedra. The kernel is protected
by four dimeric “staples” (-SR-Au-SR-Au-SR-) and eight
bridging thiolates (-SR-). The unit cell of Au28(TBBT)20 single crystals contains a pair of enantiomers. The origin
of chirality is primarily rooted in the rotating arrangement of the
four dimeric staples as well as the arrangement of the bridging thiolates
(quasi-D2 symmetry). The enantiomers were
separated by chiral HPLC and characterized by circular dichroism spectroscopy.