Unusually Short Be-Be Distances with and without a Bond in Be2F2 and in the Molecular Discuses Be2B8 and Be2B7-

摘要

Quantum-chemical calculations at the CCSD(T)/ccpVTZ level of theory show that beryllium subfluoride, Be2F2, has a bond dissociation energy of D-e=76.9 kcal mol(-1), which sets a record for the strongest Be-Be bond. The synthesis of this molecule should thus be possible in a low-temperature matrix. The discus-shaped species Be2B8 and Be2B7- possess the shortest Be-Be distance for a molecule in the electronic ground state, but there is no Be-Be bond. The cyclic species Be2B8 and Be2B7- exhibit double aromaticity with 6 sigma and 6 pi electrons, which strongly bind the Be-2 fragment to the boron atoms. The very short interatomic distance between the beryllium atoms is due to the Be-B sigma and pi bonds, which operate like spokes in a wheel pressing the beryllium atoms together. The formation of the Be-B bonds has effectively removed the electronic charge of the valence space between the beryllium atoms. Along the Be-Be axis, there are two cage critical points adjacent to a ring critical point at the midpoint, but there is no bond critical point and no bond path.