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

The Au₁₄₄(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 ¹H NMR spectroscopy can provide a detailed view of ligand-layer equivalence for thiolate protected gold nanoclusters. We show that Au ₂₅(SR)₁₈, Au₃₈(SR)₂₄ and Au ₁₀₂(SR)₄₄ nanoclusters have ¹H 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 Au₁₄₄(SR) ₆₀¹H NMR spectrum is consistent with a previously published DFT-derived structural model for Au₁₄₄(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.