Ligand symmetry-equivalence on thiolate protected gold nanoclusters determined by NMR spectroscopy

Abstract

The Au(144)(SR)(60) nanocluster has been a subject of structural conjecture since its initial description over a decade ago as a 29 kDa compound, yet a decisive empirical structure is elusive. Herein we show that (1)H NMR spectroscopy can provide a detailed view of ligand-layer equivalence for thiolate protected gold nanoclusters. We show that Au(25)(SR)(18), Au(38)(SR)(24) and Au(102)(SR)(44) nanoclusters have (1)H NMR spectra where the number of distinct chemical environments for the R-groups is equivalent to the number of symmetry environments of the sulfur headgroups, which anchor each ligand. We also show that the Au(144)(SR)(60)(1)H NMR spectrum is consistent with a previously published DFT-derived structural model for Au(144)(SR)(60). We suggest that this analysis may be extended to other structurally obscure nanoclusters, such as a ∼59 kDa compound for which we observe up to four symmetry environments.