The dominating role of 2-mercaptobenzothiazole in silver nanocluster synthesis

Abstract This work highlights the dominating role of the capping ligand 2-mercaptobenzothiazole (2-MBT) in the synthesis of silver nanocluster (AgNC). AgNC was synthesized through ligand exchange (LE) in a two phase reaction system by reacting preformed water soluble glutathione (GSH) stabilized silver nanocluster (Ag-SGNC) with 2-MBT dissolved in dichloromethane (DCM). We observed formation of a fluorescent AgNC in the organic phase from the non-fluorescent Ag-SGNC. The composition of the nanocluster was determined with the help of UV-vis, FTIR, fluorescence spectroscopy, PXRD, X-ray photoelectron spectroscopy (XPS), MALDI mass spectrometry and thermogravimetric analysis (TGA). We recently reported the formation of Ag16(2-MBT)12 cluster that was synthesized by direct reduction (DR) of AgNO3using sodium borohydride in presence of 2-MBT in a one phase reaction. Interestingly, the composition of the nanocluster synthesized through the LE reaction was determined to be the exactly same Ag16(2-MBT)12, which was synthesized by DR method. In general, syntheses of metal nanoclusters are highly susceptible to changes in reaction parameters and often results in nanoclusters of variable compositions. This showed that 2-MBT played a dominating role in the outcome of the AgNC synthesis. Moreover, we tried to justify the LE reaction and to find out a possible mechanism through time dependent study. We proposed that Ag-SGNC was etched to smaller fragments on reacting with 2-MBT. Some of these fragments where glutathione molecules were replaced by 2-MBT transferred to the organic phase from the aqueous phase. These fragments then possibly combined together to yield the thermodynamically stable Ag16(2-MBT)12 cluster.