The π···π Stacking Interactions between Homogeneous Dimers of C₆F_xI_(6–x) (x = 0, 1, 2, 3, 4, and 5): A Comparative Study with the Halogen Bond

The π···π stacking interactions between homogeneous dimers of C₆F_xI_(6–x) (x = 0, 1, 2, 3, 4, and 5) have been investigated in detail using the state-of-the-art quantum chemistry methods. Computations clearly show that the π···π stacking interaction between the homogeneous dimer of C₆F_xI_(6–x) is of the dispersion type interaction. At the same time, it is interesting to find that, for the π···π stacking interactions between homogeneous dimers of C₆F_xI_(6–x), the M05-2X/def2-TZVPP computations give almost the same results as the CCSD­(T)/SDD** computations. In the crystal growth and design, the formation of the π···π stacking interactions between homogeneous dimers of C₆F_xI_(6–x) is always accompanied by the formation of the halogen bonds. Hence, competition and cooperation of the π···π stacking interaction and the halogen bond have also been studied theoretically by using C₆F_xI_(6–x) and pyridine as coformers. At the M05-2X/def2-TZVPP theory level, it is found that the π···π stacking interactions in C₆F₅I···C₆F₅I and C₆F₄I₂···C₆F₄I₂ are weaker than the corresponding halogen bonds in C₆F₅I···NC₅H₅ and C₆F₄I₂···NC₅H₅, and the π···π stacking interactions in C₆FI₅···C₆FI₅ and C₆I₆···C₆I₆ are stronger than the corresponding halogen bonds in C₆FI₅···NC₅H₅ and C₆I₆···NC₅H₅, while the strengths of the π···π stacking interactions in C₆F₃I₃···C₆F₃I₃ and C₆F₂I₄···C₆F₂I₄ are similar to the corresponding halogen bonds in C₆F₃I₃···NC₅H₅ and C₆F₂I₄···NC₅H₅. However, when the π···π stacking interaction and the halogen bond coexist, we find that the formation of the halogen bond will lead to the π···π stacking interaction much stronger, and vice versa.