Chalcogen Bonding between Tetravalent SF4 and Amines

The N center dot center dot center dot S chalcogen bond between SF4 and a series of alkyl and arylamines is examined via ab initio calculations. This bond is a strong one, with a binding energy that varies from a minimum of 7 kcal/mol for NH3 to 14 kcal/mol for trimethylamine. Its strength derives in large measure from charge transfer from the N lone pair into the sigma*(SF) antibonding orbitals involving the two equatorial F atoms, one of which is disposed directly opposite the N atom. Decomposition of the total interaction energy reveals that the induction energy constitutes more than half of the total attraction. The positive region of the molecular electrostatic potential of SF4 that lies directly opposite the equatorial F atoms is attracted to the N lone pair, but the magnitude of this negative region on each amine is a poor predictor of the binding energy. The shortness and strength of the N center dot center dot center dot S bond in the dimethylamine center dot center dot center dot SF4 complex suggest it may better be described as a weak covalent bond.