Designing boron and metal complexes for fluoride recognition: a computational perspective.

Fluoride anions (F-) may have beneficial or harmful effects on the environment depending on their concentration. Here, we shed light on F- recognition by compounds containing boron, tellurium and antimony, which were experimentally demonstrated to be capable of interacting with the F- ion in a partially aqueous medium. Boron and metal complexes recognize F- anions primarily using electrostatic energy along with important contributions from orbital interaction energy. The natural orbitals for chemical valence (NOCV) methodology indicates that the main orbital interactions behind fluoride recognition are σ bonds between the receptors and the F- anions. The charged receptors, which provide (i) two B atoms, (ii) one B atom and one Sb atom, or (iii) one B atom and one Te atom to directly interact with the F- ions, appear to be some of the best structures for the recognition of F- anions. This is supported by the combination of favorable electrostatic and σ bond interactions. Overall, the presence of electron donor groups, such as -CH3 and -OH, in the receptor structure destabilizes the fluoride recognition because it decreases the attractive electrostatic energy and increases the Pauli repulsion energy in the receptor⋯F- bonds. Notably, electron acceptor groups, for example, -CN and -NO2, in the receptor structure favor the interaction with the F- ions, due to the improvement of the electrostatic and σ bond interactions. This study opens the way to find the main features of a receptor for F- recognition.