Halogen Bonding at High Pressure: The Case of C ₂ F ₅ I and C ₃ F ₇ I

The single-crystal structures of two in situ high-pressure crystallized analogous fluoroiodoalkanes, 1,1,1,2,2-pentafluoro-2-iodoethane (C2F5I) and 1,1,1,2,2,3,3-heptafluoro-3-iodopropane (C3F7I), were determined at room temperature and selected high-pressure points between 0.75 and 2.60 GPa. The molecules of C2F5I show disorder in the whole investigated pressure range, from 1.23 to 2.60 GPa, whereas those of C3F7I are ordered between 0.75 and 1.27 GPa. Despite the similarities in the arrangement of atoms within molecules, reflected in the same staggered conformation, these two halogenated alkanes show different interaction and packing features. Besides the F···F forces, only the molecules of C2F5I are joined together by the I···F contacts, some of which represent the very short interactions of this type for homomolecular crystals. The I···I contacts are exclusively found in C3F7I, but they first formed at a pressure of ca. 0.8 GPa.