Isomeric Thiolate Monolayer Protected Au92 and Au102 Nanomolecules

We report the results of a study of the isomeric thiolate monolayer capping of two gold nanocluster molecules, namely Au92 and Au102, both protected by 44 4-tert-butylbenzene thiolate (TBBT) ligands. The finding of an isomeric monolayer of the same ligand in a series of metal nanocluster molecules in this large size range is unprecedented. Au92 and Au102 possess entirely different structures and properties. The Au92 has an 84 atom face centered cubic (FCC) core whereas Au102 has a 79 atom Marks-decahedral core. Nevertheless, despite the metal core structural diversity and the complexities of the interfacial staples, both of these gold nanocluster molecules have the same number of ligands. The Au92 core is protected by 28 bridging ligands and 8 monomeric staple motifs whereas Au102 is protected by 19 monomeric and 2 dimeric staple motifs. The Au92 and Au102 cores have cuboidal and globular structures, respectively. As a result, Au92 has longer {100} facets and exhibits c(2 × 2) monolayer arrangement for bridging ligands similar to what has been observed on {100} facets of bulk gold, whereas Au102 has only staple motifs. We prepared the Au102 in TBBT series using a ligand-exchange-based approach and characterized them by mass spectrometry and UV-vis spectroscopy. Mass spectrometry revealed that the compound has a mixture of isoelectronic species with the formula of Au102(TBBT)44, Au103(TBBT)45, and Au104(TBBT)46. Concurrent first-principles electronic structure computational studies provide insights into the stability and nature of these two isomeric-monolayer capped gold nanomolecules.