Isolation of the Au145(SR)60X compound (R = n-butyl, n-pentyl; X = Br, Cl): novel gold nanoclusters that exhibit properties subtly distinct from the ubiquitous icosahedral Au144(SR)60 compound

Abstract

We report the identification and quantitative isolation of Au₁₄₅(SR)₆₀X (R = n-butyl, n-pentyl; X = halide) along with elucidation of key properties as compared to the corresponding ubiquitous chiral-icosahedral Au₁₄₄(SR)₆₀ 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 Au₁₄₅(SR)₆₀X behaviors that are qualitatively similar to yet fascinatingly distinct from those of Au₁₄₄(SR)₆₀. (¹H,¹³C)-NMR spectra clearly show how both Au₁₄₅(SR)₆₀X and Au₁₄₄(SR)₆₀ are capped by 12 distinct ligand types of 5-fold equivalence, as was recently established for Au₁₄₄(SR)₆₀ capped by shorter ligands, demonstrating that this novel cluster shares the same chiral-icosahedral motif. Intriguingly, Au₁₄₅(SR)₆₀X is strongly near-IR luminescent, whereas under comparable conditions Au₁₄₄(SR)₆₀ barely emits. The photoluminescence pattern of Au₁₄₅(SR)₆₀X is very similar to that observed for Au₂₅(SR)₁₈, which contains the Au₁₃ core. The combined results are interpreted as consistent with neutral Au₁₄₅(SR)₆₀X as a diamagnetic species, electronically and structurally similar to the corresponding Au₁₄₄(SR)₆₀ compounds.