Novel 2-mercaptobenzothiazole and 2-mercaptobenzimidazole-derived Ag16 and Ag18 nanoclusters: synthesis and optical properties

Silver and gold nanoclusters are promising nanomaterials for various applications such as sensing, catalysis, and bioimaging. However, their synthetic control and repeatability, and determination of their structures are highly complicated. Only a handful of crystal structures of silver nanoclusters (AgNCs) have been reported, while structures of a few others have been reported with the help of mass spectrometry. We synthesized two AgNCs, viz., Ag-MBTNC (Ag16 cluster) and Ag-MBINC (Ag18 cluster) respectively stabilized by 2-mercaptobenzothiazole (2-MBT) and 2-mercaptobenzimidazole (2-MBI) with excellent repeatability; determined their composition and plausible structures using XPS, TGA and MALDI-TOF mass spectrometry; and compared their optical properties. Interestingly, Ag-MBTNC is fluorescent while Ag-MBINC is not, although these are synthesized using stabilizing ligands that have difference in only one atom. The structural features of the clusters are found to be similar but they have contrasting optical behaviours due to the effect of one S atom (in 2-MBT) in place of one N atom (in 2-MBI).