Ab initio MP2/aug-cc-pVTZ calculations were performed to investigate charge-assisted complexes formed between a series of anions (Z- = F-, Cl-, Br-, CN-, NC-, N3-, NCS-, SCN-) and CF3X or SiF3X (X=F, CN) molecules. The nature of the interaction in these complexes, termed “anionic tetrel-bonding”, is studied by molecular electrostatic potential, noncovalent interaction, quantum theory of atoms in molecules and natural bond orbital analyses. The interaction energies of these complexes span a large range, from -1.74 kcal/mol in F4C:SCN- to -84.37 kcal/mol in (CN)F3Si:F-. The results indicate that the anionic tetrel bonds in the SiF3X complexes have a significant covalent character.
