Halogen, chalcogen and pnictogen interactions in (XNO₂)₂ homodimers (X = F, Cl, Br, I)

A theoretical study of the XNO₂ homodimers (X = F, Cl, Br and I) has been carried out by means of the Møller-Plesset (MP2) methodology. Twenty-two different minimum structures have been found, involving pnictogen, chalcogen and halogen bonds. MP2 interaction energies range between -0.4 to -17.5 kJ mol^-1. Atoms in molecules (AIM) and natural bond orbital (NBO) approaches have been used to analyse the nature of the interaction within both monomers, obtaining good correlations between Laplacian values and bond distances. NBO E(2) orbital interaction energies are found to be up to 39.0 kJ mol^-1. Charge transfer between monomers is in agreement with those in AIM and NBO findings, showing the highest charge transferred in those asymmetric dimers which involve pure halogen bonds. Symmetry adapted perturbation theory (SAPT-DFT) results show that the interactions are driven by the dispersion term, followed by the electrostatic one. The induction term presents the lowest contribution with the exception of complexes 1 and 5 of the iodine derivative in which E_i⁽²⁾ shows the maximum contribution to the total forces.