Redefining the Term of “Cocrystal” and Broadening Its Intention

"Cocrystal" is currently an increasingly popular term in the crystal community, as it has already been verified that the cocrystallization to form new crystals can serve as a promising strategy and an efficient technology to modulate and improve properties and performances of materials in the fields of pharmaceuticals and others. Nevertheless, the definition and intetsion of cocrystal still remain debatable. In this Perspective, we redefine cocrystal with a broadened intention as "a cocrystal is a single-phase crystalline solid composed of two or multiple components in a stoichiometric ratio, and the components of a cocrystal can be atoms, molecules, anions and cations in pairs, and/or metallic cations with free electrons shared". Thereby, cocrystals are classified into five types in terms of the kinds of the components and their interactions in crystal entity, including atomic cocrystal, molecular cocrystal, ionic cocrystal, metallic cocrystal, and mixed-type cocrystal. The reasserted definition and broadened intention of cocrystal present a uniform term for all crystalline solids with two or multiple components and help to avoid confusion of numerous existing terms of these solids. Thereby, some terms with narrow intentions are expected to be updated and applied less and less as time goes on.