Cluster-π Interactions Cause Size-Selective Reactivity of Cationic Silver Clusters with Acetylene: The Distinctive Ag[CH].

Utilizing a customized multiple-ion laminar flow tube reactor in tandem with a triple quadrupole mass spectrometer, we report a study of the gas-phase reactivity of Ag clusters with acetylene. Well-resolved Ag clusters ( = 1-20) are produced by a self-designed magnetron sputtering source (MagS); however, on their reactions with acetylene under sufficient collisional conditions, only Ag[CH] is produced with a reasonable intensity. DFT calculations reveal that Ag clusters do not form strong Ag-C bonds with CH and Ag[CH] bears larger binding energy than the other Ag[CH] although within similar cluster-π interactions. Besides gas-phase reaction rate estimation, the relatively large noncovalent cluster-π interaction in Ag[CH] is fully demonstrated via topological analysis and natural bonding orbital analysis. Also, we illustrate both thermodynamically and kinetically favored channels in producing the Ag[CH]. This study helps in understanding metal-involved noncovalent bonds and how such weak interactions are able to tune the material function and biological activity.