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 Be2 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-1) 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-1). The latter has been used to determine a lower bound of 343 kJ mol-1 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.