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{sub 7} cluster. Here we show in detail that a unique series of silver sulfide cluster anions (Ag{sub n}S{sub 4}{sup -}) were observed sequentially from n = 7 to 1 when subjecting the thiolate-protected Ag{sub 7} cluster to an MS/MS experiment. Random silver cluster anion distributions were not observed in a wide range of collision energies. This indicates the special structure and stability of these gas phase Ag{sub n}S{sub 4}{sup -} clusters. Global minimum search based on density functional theory-enabled basin hopping has yielded the most stable structures for Ag{sub n}S{sub 4}{sup -} (1 {le} n {le} 7). The global minima show a transition from three-dimensional to two-dimensional and then to one-dimensional geometry with decreasing n for Ag{sub n}S{sub 4}{sup -} clusters. This joint experimental and computational effort provides a pathway to discover and elucidate metal-sulfide clusters of unique stoichiometry, which are not accessible through conventional methods such as laser ablation of mixed metal and sulfur powders.