New Type of Halogen Bond involving Multivalent Astatine: An Ab Initio Study

Theoretical researches on the dimers formed by CO with halides of the multivalent astatine as a Lewis-acid center are conducted to examine the typical characteristics of supervalent halogen bond. Calculation on MP2/aug-cc-pVTZ level reveals that the multiple nucleophilic sites of multivalent halide monomers can promote the formation of various types of halogen bonds, among which the most stable ones are At-halogen bond complexes with the multivalent astatine as Lewis acid center, followed by the π-halogen bond dimers, and the weakest are the X-halogen bonds. Compared with multivalent Cl-, Br-, and I-center, At, as the heaviest halogen, exhibits the highest halogen-bond donating ability. We found that the greatest contribution to the total interaction energy is originated from the exchange energy, with the electrostatic term and the dispersion term also playing an important role in the overall attractive bonding energy. Moreover, the tri and pentavalent halides analyzed here possess the very “flexible” tautomerism that the transformation occurs during the formation of the dimers. AIM theory and NBO analysis are also applied here.