The Smallest Thiolated Gold Superatom Complexes

The superatom concept of metallic cluster valence is based on the electron-shell model as first proposed to explain the special stability of certain metal-atom clusters generated in the gas phase. It accounts for the magic-number series 2, 8, 18, 34, 58, ... by shell-closing of the superatom orbitals 1S, 1P, 1D, .... Recently, the superatom-complex concept has been introduced to explain the compositions of high-yield gold-cluster compounds, especially Au 25 (SR) 18 − and Au 102 (SR) 44 (with -SR being a thiolate group), corresponding to the magic numbers of 8 and 58, respectively. Surprisingly, no thiolated gold cluster accounting for the first closing (electron count 2) has yet been determined. Structure-bonding considerations lead us to propose Au 12 (SR) 9 + as the superior candidate for the smallest thiolated gold superatom. This cluster features an octahedron core covered by three RS(AuSR) 2 motifs. It has a unique C 3 axis, is chiral, and possesses ideal aurophilic interactions and, therefore, should exist in nature. The folding of thiol-rich biomolecules may help us to realize this complex, which may also be prepared from available phosphine-ligated gold clusters.