The π···π stacking interactions between homogeneous dimers of C6F(x)I((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 C(6)F(x)I((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 C(6)F(x)I((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 C(6)F(x)I((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 C(6)F(x)I((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 C(6)F(x)I((6-x)) and pyridine as coformers. At the M05-2X/def2-TZVPP theory level, it is found that the π···π stacking interactions in C(6)F(5)I···C(6)F(5)I and C(6)F(4)I(2)···C(6)F(4)I(2) are weaker than the corresponding halogen bonds in C(6)F(5)I···NC(5)H(5) and C(6)F(4)I(2)···NC(5)H(5), and the π···π stacking interactions in C(6)FI(5)···C(6)FI(5) and C(6)I(6)···C(6)I(6) are stronger than the corresponding halogen bonds in C(6)FI(5)···NC(5)H(5) and C(6)I(6)···NC(5)H(5), while the strengths of the π···π stacking interactions in C(6)F(3)I(3)···C(6)F(3)I(3) and C(6)F(2)I(4)···C(6)F(2)I(4) are similar to the corresponding halogen bonds in C(6)F(3)I(3)···NC(5)H(5) and C(6)F(2)I(4)···NC(5)H(5). 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.