Sequential Observation of AgnS4- (1 ≤ n ≤ 7) Gas Phase Clusters in MS/MS and Prediction of Their Structures

Recently we reported synthesis and characterization of a monodisperse thiolate-protected Ag-7 cluster. Here we show in detail that a unique series of silver sulfide cluster anions (AgnS4-) were observed sequentially form n = 7 to 1 when subjecting the thiolate-protected Ag-7 cluster to an MS/MS experiment. Random silver cluster anion distribution were not observed in a wide range of collision energies. This indicates the special structure and stability of these gas phase AgnS4- clusters. Global minimum search based on density functional theory-enabled basin hopping has yielded the most stable structures for AgnS4- (1 <= n <= 7). The global minima show a transition from three-dimensional to two-dimensional and then to one-dimensional geometry with decreasing n for AgnS4- clusters. This joint experimental and computational effort provides a pathway to discover and elucidate metal-sulfide cluster of unique stoichiometry, which are not accessible through conventional methods such as laser ablation of mixed metal and sulfur powders.