First-Principles Crystal Engineering of Nonlinear Optical Materials. II. Effect of Halogen Bonds on the Structure and Properties of Triiodobenzenes

Recently, we proposed a computational design strategy for organic nonlinear optical materials, based on the global minimization of lattice energy to predict the crystal packing from the first principles. Here, we validate this strategy on triiodobenzenes, which include CH···I hydrogen and I···I halogen bonding as the structure-determining components of their intermolecular interactions. To refine the van der Waals (vdW) parameters for an I atom, the ab initio potential surfaces for the model dimers were calculated at the CCSD(T)/cc-pVTZ + CP theory level. The hydrogen bond C–H···I was found to have an interaction energy of −0.5 kcal/mol. The I···I contact of type I (140°–140°) was found to be attractive with a well depth of −0.4 kcal/mol at a 4.6 A distance, whereas type II contact (180°–90°) was found to be nearly twice more attractive. Its potential well depth reaches −0.7 kcal/mol at an I···I distance of 4.4 A. These binding energies are therefore weaker than that of the typical hydrogen bonds. The AMO...