A computational investigation of halogen bonding with halomethanes and their group 14 analogues

It is known that halogen bonding is supported by so-called sigma holes on halides that interact with bases, but what are the limits of that interaction? How does the interaction depend on the group to which the halogen atom is bonded? To answer these questions, complexes of the form MH3X---Y (where M=C, Si, Ge, Sn, Pb; X= F, Cl, Br, I and Y are Lewis bases) were optimized and their energetics and relative stability were assessed. The Lewis bases range from NH3 to the more complicated pentafluroropyridine (F-py). Calculations were performed entirely at the MP2(full) level of theory, including frequency analyses for the complexes. Additionally, their electrostatic potentials and interaction energies were used to determine the stability (or presence) of a halogen bond. Moderately strong halogen bonds are formed by some of these complexes, but quite weak halogen bonds and alternative interactions – evidently more favorable than halogen bonding - have been observed