An ultrastable thiolate/diglyme ligated cluster: Au20(PET)15(DG)2.

Abstract

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.