Organic solvents enable handedness control in inorganic crystals

Chirality—often described as “handedness”—is a fundamental property of nature, underlying the behavior of molecules ranging from DNA to pharmaceuticals. While chemists have long known how to separate left- and right-handed forms of organic compounds, achieving the same control in inorganic crystals has remained a major scientific challenge.

Researchers at Kumamoto University have now demonstrated a simple and effective way to control the handedness of an inorganic crystal using organic solvents and an unexpected crystalline “helper”—an achiral crystalline phase. Their study shows that cesium copper chloride (CsCuCl₃), a chiral inorganic material known for its unique magnetic and optical properties, can be crystallized into single-handed forms under relatively mild conditions.

Normally, CsCuCl₃ grown from water forms racemic twin crystals—intergrowths of both left- and right-handed domains—making it difficult to isolate a single chiral form. The research team found that adding small amounts of organic solvents, such as ethylene glycol or 1-pentanol, dramatically changes the crystallization process. Under these conditions, CsCuCl₃ forms enantiopure single crystals, containing only one handedness.

Detailed structural analysis revealed that the organic solvents alter how the crystal grows, suppressing growth along certain directions and preventing the mixing of opposite chiral domains. In addition, the researchers discovered that an achiral crystalline phase, Cs₃Cu₃Cl₈(OH), can appear during crystallization. Remarkably, when this achiral crystal was used as a seed, it induced the growth of homochiral CsCuCl₃ on its surface.

The ability to prepare homochiral CsCuCl₃ is particularly important because the material exhibits magnetochiral and quantum magnetic properties that depend sensitively on its handedness. Beyond this specific compound, the findings suggest a broadly applicable strategy for controlling chirality in inorganic materials using solvent choice and crystallization pathways.

The study provides new insight into how subtle changes in crystal growth environments can generate symmetry breaking in solid materials—an advance that may support future developments in functional materials, spintronics, and chiral separation technologies.