Isolation of the Au(SR)X compound (R = -butyl, -pentyl; X = Br, Cl): novel gold nanoclusters that exhibit properties subtly distinct from the ubiquitous icosahedral Au(SR) compound.

We report the identification and quantitative isolation of Au(SR)X (R = -butyl, -pentyl; X = halide) along with elucidation of key properties as compared to the corresponding ubiquitous chiral-icosahedral Au(SR) cluster known to have a central vacancy. The stoichiometries were assessed by electrospray mass spectrometry (ESI-MS) at isotopic resolution, and induced dissociation patterns indicate the 'extra' (Au,Br) atoms are strongly bound components of these structures. Voltammetric and spectroscopic characterization reveals Au(SR)X behaviors that are qualitatively similar to yet fascinatingly distinct from those of Au(SR). (H,C)-NMR spectra clearly show how both Au(SR)X and Au(SR) are capped by 12 distinct ligand types of 5-fold equivalence, as was recently established for Au(SR) capped by shorter ligands, demonstrating that this novel cluster shares the same chiral-icosahedral motif. Intriguingly, Au(SR)X is strongly near-IR luminescent, whereas under comparable conditions Au(SR) barely emits. The photoluminescence pattern of Au(SR)X is very similar to that observed for Au(SR), which contains the Au core. The combined results are interpreted as consistent with neutral Au(SR)X as a diamagnetic species, electronically and structurally similar to the corresponding Au(SR) compounds.