Variations of quantum electronic pressure under the external compression in crystals with halogen bonds assembled in Cl₃-, Br₃-, I₃-synthons

The inner-crystal quantum electronic pressure was estimated for unstrained C₆Cl₆, C₆Br₆, and C₆I₆ crystals and for those under external compression simulated from 1 to 20 GPa. The changes in its distribution were analyzed for the main structural elements in considered crystals: for triangles of the typical halogen bonds assembled in Hal₃-synthons, where Hal = Cl, Br, I; for Hal...Hal stacking interactions, as well as for covalent bonds. Under simulated external compression, the quantum electronic pressure in the intermolecular space reduces as the electron density increases, indicating spatial areas of relatively less crystal resistance to external compression. The most compliant C₆Cl₆ crystal shows the largest changes of quantum electronic pressure in the centre of Cl₃-synthon while the deformation of rigid I₃-synthon under external compression depends only on the features of I...I halogen bonds.