Utilizing Co-Crystallization as a Tool to Unravel the Structural Diversity and Electronic Features of I...S Halogen Bonded Interactions in Stoichiomorphic Co-Crystals

In the current investigation, we report five new co-crystals formed by combinations of triphenylphosphine sulfide (PS) with 1,3,5-triiodo-2,4,6-trifluorobenzene (I3F), triphenylphosphine sulfide (PS) with 1,4-diiodotetrafluorobenzene (IF) which consists of I-centered interactions, primarily consisting of I ... S halogen bonding interactions. The distance between the iodine and sulfur atoms in the different crystal structures is much shorter than the sum of the van der Waals radii (shortest I ... S distance, 3.163 angstrom) and is highly directional (most directional C-I ... S, 179 degrees) in nature. The three-dimensional deformation density shows that the charge depleted (CD) region on iodine electrostatically interacts with the charge concentrated (CC) region on sulfur. The interaction energy, as obtained from density functional theory calculations, is in the range of -16 to -32 kJ/mol, for the interacting units, at the crystal geometry. The atomic polarizability analysis establishes the mutual polarization of the iodine atom in the presence of the sulfur atom and vice versa. A topological analysis unequivocally establishes the presence of a (3, -1) bond critical point, and the NCI-RDG analysis establishes the attractive nature of the interaction. The elongation of the C-I bond length as a consequence of evident charge transfer from sulfur to iodine for I...S interaction is computed via natural bonding orbitals. Thus, a detailed computational analysis renders insights into the electronic nature of the observed I...S interactions in the solid state.