Dynamic Diglyme-Mediated Self-Assembly of Gold Nanoclusters.

Self-assembly of gold nanoparticles mediated by thiolate ligands such as DNA oligonucleotides enables both fundamental and applied studies on the resulting superstructures. We report generalized assembly of gold nanoclusters by the non-thiolate ligand diglyme into discrete and dynamic structures. To understand this surprising phenomenon, the assembly of Au20(SC2H4Ph)15-diglyme into Au20(SC2H4Ph)15-diglyme-Au20(SC2H4Ph)15 is explored in detail. The assembly is validated by size exclusion chromatography, mass spectrometry, IR spectroscopy, calorimetry, and high-angle annular dark field scanning transmission electron microscopy. We establish a dissociation constant for dimer to monomer conversion of 20.4 µM. Theoretical models validated by transient absorption spectroscopy predict a low-spin monomer and a high-spin dimer, with assembly enabled through weak diglyme oxygen-gold interactions. Close spatial coupling allows electron delocalization between the nanoparticle cores. The resulting assemblies thus possess emergent optical, electronic, and structural properties.