Redefining the Term of “Cocrystal” and Broadening Its Intention

Abstract

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.

Melting points of one- and two-component molecular crystals as effective characteristics for rational design of pharmaceutical systems

“…Despite numerous studies, the nature of co-crystallization remains inadequately understood. Moreover, understanding and controlling the main driving forces of co-crystal formation is a significant fundamental task (Zhang et al, 2019). Any co-crystal is, in principle, structurally modular.…”

Syntheses, Crystal Structures, and Properties of Two Novel CL‐20‐based Cocrystals

“…The definition of cocrystal has remained debatable. Recently, Zhang et al redefine cocrystal with a broadened intention as “a cocrystal is solid that is crystalline single phase material composed of two or multiple components in a stoichiometric ratio, and the components can be atoms, molecules, anions and cations in pairs, and / or metallic cations with free electrons shared.”…”

Anion Influence on the Packing of 1,3-Bis(4-Ethynyl-3-Iodopyridinium)-Benzene Halogen Bond Receptors

“…These crystalline materials, which contain two or more individual molecular components, frequently exhibit altered physiochemical properties compared to the individual components [8][9][10], highlighting their value to many industries. As interest in multicomponent solids has increased, the need for more specific classifications has grown, resulting in (currently) conflicting nomenclature [11][12][13]. Forgoing terminology discussions, the use of formal charges to build multicomponent solids is an appealing tactic, as charge balance necessitates the presence of two molecular entities (unless zwitterionic in nature).…”