Stable Tetra‐ and Penta‐Anions in the Gas Phase

Abstract

The quest for stable gas-phase anions in highly negative charge states has been ag reat challenge.W hile multiply charged anions are stabilized in solids and liquids by compensating cations and solvation cells,respectively,stable anions containing less than ah undred atoms in the gas phase and capable of carrying charge beyond À3isunknown. Here, we report the discovery of thermodynamically stable tetra-and penta-anions,c ontaining less than 50 and 80 atoms,r espectively,i nt he gas phase.Auniversal model is developed that explains their stability in terms of the synergy between closed shell, high electron affinity,a nd size and predicts new highlycharged anions by using the known charged clusters as building blocks.S ynthesis of these species can open an ew chapter in materials chemistry.The enhanced stability of ac losed shell atom lies in the quantum mechanical interactions between electrons.E lectrons with the same spins tend to avoid each other, thereby reducing the Coulomb repulsion between them. Therefore, ac losed-shell atom, that is,a na tom with every spin being paired, gains extra stability.T he closed-shell model provides agood explanation for the reactivity of atoms that are only an electron away from the closed shell. Fore xample,ahalogen (Group 17) atom with asingle hole tends to form astable core by gaining one electron from another atom having aw eakly bound unpaired electron, such as an alkali (Group 1). In fact, the mono-anionic state of ah alogen is more stable than its neutral state,a ss hown by its positive electron affinity (EA) defined by