Superatomic 1S orbital-mediated ethylene activation on Ag<i>n</i>− clusters

Single-cluster catalysts (SCCs) leverage superatomic properties via well-defined geometric/electronic configurations to enable novel reactions. The development of SCCs has facilitated atomic-level insights into catalyst design, thereby advancing our understanding of the fundamental nature of catalytic reactions. While orbital symmetry rules guide unimolecular catalyst design, the role of superatomic orbital symmetry in SCC reactivity remains elusive. Herein, we systematically investigated the gas-phase reactions of Agn- (n = 7-25) clusters with C2H4, employing a combination of time-of-flight mass spectroscopy and density functional theory calculations. This revealed strong size-dependent reactivity: Ag7-11, 18-23- showed remarkable stability, whereas Ag12-17, 24-25- adsorbed one or even two C2H4 molecules. The electron clouds of 1S superatomic orbital in Ag12-15, 24-25- clusters are partially localized on specific atoms. This partial localization enables effective interactions between the 1S orbital and the π orbital of C2H4, while concurrently enhancing stability through the formation of bonding orbitals and the d-orbital coupling among silver atoms. Notably, C2H4 adsorption induces structural reorganization of Ag16, 17-, resulting in the formation of icosahedral cages. These cages contain highly symmetrical electron clouds that provide symmetrically matched orbitals, favoring secondary C2H4 adsorption and thereby enhancing the stability of complexes. Our research introduces a novel framework for the precision engineering of superatomic clusters while broadening the application scope of the superatomic properties of metal clusters. The discovery of the superatomic orbital symmetry rule sheds light on the activity series of SCCs and offers new insights into precise SCC engineering.