Dative Bonding between Closed-Shell Atoms: The BeF Anion.

Beryllium can exhibit unusually strong attractive interactions under conditions where it is nominally a closed-shell atom. Two prominent examples are the Be dimer and the He-BeO complex. In the present study, we examine the bonding of the closed-shell Be-F anion. This molecule preserves the closed-shell character of the individual atoms as the electron affinity of F is high (328.16 kJ mol) while that of Be is negative. Photodetachment spectroscopy was used to determine the vibrational frequency for BeF and the electron affinity of BeF (104.2 kJ mol). The latter has been used to determine a lower bound of 343 kJ mol for the bond energy of BeF. Electronic structure calculations yielded predictions that were in good agreement with the observed data. A natural bond orbital analysis shows that BeF is primarily bound by a dative interaction.