Unexpected strong stacking interactions between the homogeneous dimers of C6FxI(6−x) (x = 0, 1, 2, 3, 4 and 5)

The stacking interactions between the homogeneous dimers of C6FxI(6−x) (x = 0, 1, 2, 3, 4 and 5) have been reinvestigated in the present study. Using the tetraiodoethylene dimer as a model for the homogeneous dimers of C6FxI(6−x), we compared the potential energy curves of different computational methods with the benchmark at the coupled-cluster method with iterative single and double excitations, and perturbative correction for the triples, CCSD(T), in the complete basis set (CBS) limit. The results clearly show that the ωB97X-D/def2-TZVPP, B2PLYP-D/def2-TZVPP, and SCS-MP2/aug-cc-pVQZ calculations give almost the same potential energy curves as the CCSD(T)/CBS benchmark. Finally, the ωB97X-D/def2-TZVPP method is recommended for studying the stacking interactions between the homogeneous dimers of C6FxI(6−x) due to its less computational demands (CPU time, memory, storage). It is also found that the difference between the real CCSD(T) value and the estimated CCSD(T) value can be up to 2 kcal/mol, which indicates that the estimated CCSD(T) values should be used carefully. At the reliable ωB97X-D/def2-TZVPP level of theory, the interaction energies for the homogeneous dimers of C6FxI(6−x) range from about −7.00 kcal/mol to −17.00 kcal/mol. These values are considerably larger than previously calculated ones. The results show that, besides the aromatic stacking interaction, the I⋯I interaction also plays an important role for the stabilization of the homogeneous dimers of C6FxI(6−x).