On the formation of beryllium bonds where radicals act as electron donors

The complexes between BeX2 (X = F, H) with CH3, CH2CH3, CH(CH3)(2) and C(CH3)(3) radicals have been characterized by using the MP2 and CCSD(T) methods and AIM procedure. The formation of these complexes is found to originate from the interaction between the positively charged Be atom and the unpaired electron of the radicals, and this interaction is closed shell in essence. During complexation with radicals, all the BeX2 molecules feature redshifted X-Be-X antisymmetric stretching vibrations, according well with the lengthening of Be-X bonds. According to the computed interaction energies, methyl substitution imposes a positive effect on the complex formation. Energy decomposition analysis indicate that the stability of the topic complexes mainly comes from the attractive electrostatic and polarization terms, which is similar to the case of pi-beryllium bonds. By comparisons with some related systems, it can be concluded that the bond strength increases in the order single-electron hydrogen bond < single-electron sodium bond < single-electron lithium bond < single-electron beryllium bond approximate to pi-beryllium bond.