The nature of the I⋯I interactions and a comparative study with the nature of the π⋯π interactions

The I⋯I interactions play an important role in molecular self-assembly. In the present study, the nature of the I⋯I interactions has been investigated and compared with the nature of the π⋯π interactions by using the I2 dimer and benzene dimer as the prototypes of these interactions. The CCSD(T) interaction energies in the complete basis set limit at the equilibrium distances are −1.51, −2.04, and −3.08 kcal/mol for the sandwich, parallel-displaced, and T-shaped configurations of the I2 dimer, respectively. These energy values are little different from the corresponding ones of the benzene dimer. In addition to accurate interaction energies, we have also performed symmetry adapted perturbation theory analyses for the sandwich, parallel-displaced, and T-shaped configurations of the I2 dimer and benzene dimer. The dispersion interaction was found to be the major source of attraction in the sandwich and parallel-displaced configurations of the I2 dimer and benzene dimer. Different from the T-shaped configuration of the benzene dimer in which the dispersion interaction is still the major source of attraction, electrostatic, induction and dispersion interactions play equal role for the stabilization of the T-shaped configuration of the I2 dimer. On the other hand, potential energy curves for the sandwich, parallel-displaced, and T-shaped configurations of the I2 dimer were obtained employing different wave function and density functional theories with several large basis sets. It was noted that, for the T-shaped configuration of the I2 dimer, all the theory methods considered in this work cannot give comparable results to the CCSD(T) ones in the complete basis set limit. Relationships between the nature of the I⋯I and π⋯π interactions and the performance of theory methods were discussed.