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

We report herein a class of superatomic AU13 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 AU13 cluster[Au1g(NHC-1)sBr6],which has bulky NHC-1 ligands that lead to a rather open metal surface contributing to its high catalytic activity;(2)the tricationic cluster[Au13(NHC-2)sBr2]+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:a(NHC-3)gClg]f+exhibits reversible and stable visible absorption and solubility responses to protonation/deprotonation cycles,making it a potential pH sensor(NHC-1=1,3-disopropylbenzimidazolin-ylidene;NHC-2=1,3-bis(1-benzyl-1H-benzimidazol-1-ium-yl)propane;NHC-3=1,3-bis(icolyI)benzimidazolin-ylidene).The study nicely demonstrates the importance of ligands in designing metal nanoclusters with desired functionalities.