Comparison of the directionality of the halogen, hydrogen, and lithium bonds between HOOOH and XF (X = Cl, Br, H, Li).

Detailed electrostatic potential (ESP) analyses were performed to compare the directionality of halogen bonds with those of hydrogen bonds and lithium bonds. To do this, the interactions of HOOOH with the molecules XF (X = Cl, Br, H, Li) were investigated. For each molecule, the percentage of the van der Waals (vdW) molecular surface that intersected with the ESP surface was used to roughly quantify the directionality of the halogen/hydrogen/lithium bond associated with the molecule. The size of the region of intersection was found to increase in the following order: ClF < BrF < HF < LiF. The maximum ESP in the region of intersection, V S, max, was observed to become more positive according to the sequence ClF < BrF < HF < LiF. For ClF and BrF, the positive electrostatic potential was concentrated in a very small region of the vdW molecular surface. On the other hand, for HF and LiF, the positive electrostatic potential was more diffusely scattered across the vdW surface than for ClF and BrF. Also, the optimized geometries of the dipolymers HOOOH··· XF (X = Cl, Br, H, Li) indicated that halogen bonds are more directional than hydrogen bonds and lithium bonds, consistent with the results of ESP analyses.