Exceptionally Strong Triply Dative Be-F Bonds in [CO]BeF and [CO]BeF Complexes: Reducing Valence Shell Electron Repulsion to Achieve High Bond Dissociation Energies.

Dative bonds are typically polar, weaker, and longer than electron-sharing covalent bonds. The intriguing diatomic BeF anion uniquely exhibits triple Be-F dative bonding with a considerable bond dissociation energy (BDE) of 88 kcal/mol. Here, we report exceptionally strong dative-bonded systems, [CO]BeF and [CO]BeF, with BDE values exceeding 155 kcal/mol by integrating [CO] and [CO] groups into the BeF framework. These designed -symmetric molecules represent the lowest-energy configurations and maintain similar triply bonded Be-F interactions with orbital characteristics and bond distances closely resembling those in BeF. Chemical bonding analysis reveals that [CO] and [CO] groups significantly withdraw s-type nonbonding electrons from Be, which minimizes valence shell electron repulsion from the F to Be interactions. This reduction in Pauli repulsion between the closed-shell fragments in [CO]BeF and [CO]BeF, compared to that of BeF, establishes a new record in dative bond strength and offers substantial insights into dative bonding mechanisms. The identified high thermodynamic and kinetic stability of these systems positions them as promising candidates for experimental detection in low-temperature matrices or the gas phase.