The effects of P-T changes on intermolecular interactions in crystal structure of iodoform

The structural transition at different pressures of a halogen and hydrogen bonded molecular structure (iodoform, CHI3) is described. The pressures analyzed up to sample decomposition are 0.85 GPa (P1RT) and 2.15 GPa (P2RT); also room conditions (P0RT) and low temperature (106 K, P0LT) structures have been reported for comparison. The observed disorder-order phase transition, from P63/m to P63 space group, can be rationalized by the intermolecular interaction analysis. The shortening of the distances among iodoform planes, observed during the compression and the temperature decreasing, determines an ordering of molecular dipoles in a parallel arrangement: this phase transition causes a shortening of I⋯I halogen bondings. The BSSE corrected cohesive energies have been calculated for all structures at DFT/B3LYP level of theory using a periodic boundary condition code and the Grimme dispersion correction. Hirshfeld surfaces and electrostatic potential mapped on charge density isosurfaces have been computed and their features have been analyzed, in order to better understand the halogen intermolecular interactions that control the structural modification of iodoform crystal.