The Au25(pMBA)17Diglyme Cluster

Effects of Diglyme on Au Nanocluster Formation: Mechanism, 1H NMR, and Bonding

Recently, diglyme was applied as a solvent in the synthesis of a luminescent gold-thiolate nanocluster. However, the interactions between the diglyme and the gold nanocluster and the intrinsic mechanism of the diglyme-assisted nanocluster growth have not been examined. In this work, we use density functional theory (DFT) to propose a plausible pathway for diglyme-assisted Au(I)-thiolate synthesis; the reaction energies are found to be negative in every step. ¹H NMR calculations are applied to characterize how the environment arising from different gold motifs affects the chemical shifts of the protons on diglyme, which experience strong downfield shifts. Extended transition state-natural orbitals for chemical valence (ETS-NOCV) theory is also utilized to examine the interactions between diglyme and gold clusters as well as a Au₂₀(SR)₁₅ nanocluster. Our work demonstrates that diglyme can play an important role in the synthetic mechanism yielding gold nanoclusters and provides insights into the diglyme-nanocluster binding motifs and resulting NMR chemical shifts.

An ultrastable thiolate/diglyme ligated cluster: Au20(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.