Superatomic Au13 clusters ligated by different N-heterocyclic carbenes and their ligand-dependent catalysis, photoluminescence, and proton sensitivity

We report herein a class of superatomic Au-13 clusters stabilized by different N-heterocyclic carbenes (NHCs). The clusters show diverse metal surface structures, properties and functions as exemplified by: (1) the first anionic Au-13 cluster [Au-13(NHC-1)(6)Br-6](-), which has bulky NHC-1 ligands that lead to a rather open metal surface contributing to its high catalytic activity; (2) the tricationic cluster [Au-13(NHC-2)(5)Br-2](3+) which has bidentate, benzyl-rich NHC-2 ligands that make it ultra-stable and highly-luminescent, suitable for bio-imaging; and (3) by bearing two pyridyl groups on NHC-3, the dicationic cluster [Au-13(NHC-3)(9)CI3](2+) exhibits reversible and stable visible absorption and solubility responses to protonation/deprotonation cycles, making it a potential pH sensor (NHC-1 = 1,3-diisopropylbenzimidazolin-2-ylidene; NHC-2 = 1,3-bis(1-benzyl-1H-benzimidazol-1-ium-3-yl)propane; NHC-3 = 1,3-bis(picolyl)benzimidazolin-2-ylidene). The study nicely demonstrates the importance of ligands in designing metal nanoclusters with desired functionalities.