Anion–anion interactions: their nature, energy and role in crystal formation

Theoretical and experimental data array confirming the possibility of occurrence of bonding interactions in a crystal between like-charged species, namely anions, that contribute significantly to the crystal packing formation is analyzed. The main types of anion–anion interactions, their strength and contribution to the stabilization of ionic crystals are systematically analyzed for a wide range of organic and inorganic salts. The potential of various theoretical and experimental methods of investigations aimed at detection of anion–anion interactions and estimation of their energy is discussed.