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 Hal(3)-synthons, where Hal = Cl, Br, I; for Hal center dot center dot center dot 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 Cl-3 synthon while the deformation of rigid I-3-synthon under external compression depends only on the features of I center dot center dot center dot I halogen bonds.