Anticooperativity of Multiple Halogen Bonds and Its Effect on Stoichiometry of Cocrystals of Perfluorinated Iodobenzenes

on the remaining iodine atoms and dramatically decreases their potential for forming further halogen bonds, which explains both the high occurrence of crystal structures where the donors do not achieve their maximal topicity and the observed differences in halogen bond lengths. Despite the fact that this effect increases with the basicity of the acceptor, when the increase of halogen bond energy due to the basicity of the acceptor compensates its decrease due to the reduction of the acidity of the donor, it enables strong bases to form cocrystals in which a potentially polytopic XB donor achieves its maximal topicity.