An ultrastable thiolate/diglyme ligated cluster: Au ₂₀ (PET) ₁₅ (DG) ₂

The synthesis and characterization of an Au₂₀(PET)₁₅(DG)₂ (PET = phenylethane thiol; DG = diglyme) cluster is reported. Mass spectrometry reveals this as the first diglyme ligated cluster where diglyme ligands survive ionization into the gas phase. Thermal analysis shows the cluster degrades at 156 °C, whereas the similar Au₂₀(PET)₁₆ cluster degrades at 125 °C, representing markedly increased thermal stability. A combination of NMR spectroscopy and computational modeling suggests that the diglyme molecules bind in a tridentate manner for this cluster, resulting in a binding energy of 35.2 kcal mol^-1 for diglyme, which is comparable to the value of ∼40 kcal mol^-1 for thiolates. IR and optical spectroscopies show no evidence of assembly of this cluster, in contrast to Au₂₀(PET)₁₅(DG), which readily assembles into dimeric species, which is consistent with a tridentate binding motif. Evidence for stacking among Au-bound and non-bound diglyme molecules is inferred from thermal and mass analysis.