Are Anions of Cyclobutane Beryllium Derivatives Stabilized through Four-Center One-Electron Bonds?

High-level G4 ab initio calculations allowed us to show that C₄H₄(BeX)₄ (X = H, Cl) derivatives behave as rather efficient electron capturers due to their ability to trap the extra electron through the formation of a four-membered beryllium ring. This finding is in agreement with previous work showing the ability of highly electron-deficient atoms, such as beryllium, to lead to multicenter one-electron bonds. In our particular case, the formation of the four-center bond is characterized, in very good harmony, by different topological methods such as quantum theory of atoms in molecules (QTAIM), the electron localization function (ELF), and the noncovalent interactions (NCI) approach and is accompanied by large electron affinity values, around 300 kJ·mol^-1, in the gas phase. Preliminary results may anticipate that the ability of groups of beryllium atoms to trap electrons decays on going to bigger systems.