The Role of Molecular Electrostatic Potentials in the Formation of a Halogen Bond in Furan•••XY and Thiophene•••XY Complexes

The halogen bonding of furan center dot center dot center dot XY and thiophene center dot center dot center dot XY (X = Cl, Br; Y = F, Cl, Br), involving sigma- and pi-type interactions, was studied by using MP2 calculations and quantum theory of atoms in molecules (QTAIM) studies. The negative electrostatic potentials of furan and thiophene, as well as the most positive electrostatic potential (V-S,V-max) on the surface of the interacting X atom determined the geometries of the complexes. Linear relationships were found between interaction energy and V-S,V-max of the X atom, indicating that electrostatic interactions play an important role in these halogen-bonding interactions. The halogen-bonding interactions in furan center dot center dot center dot XY and thiophene center dot center dot center dot XY are weak, closed-shell noncovalent interactions. The linear relationship of topological properties, energy properties, and the integration of interatomic surfaces versus V-S,V-max of atom X demonstrate the importance of the positive sigma hole, as reflected by the computed V-S,V-max of atom X, in determining the topological properties of the halogen bonds.