Organoferroelasticity Mediated by Water of Crystallization

Despite the general conception of brittleness, organic single crystals composed of various kinds of molecules can show ferroelasticity by mechanical twinning. This is attributed to flexibilities in molecular structures, e.g., conformation, and noncovalent bonds, e.g., length and angle. Herein, we find ferroelasticity by mechanical twinning mediated by water of crystallization in a single crystal of a zwitterion: sulfanilic acid monohydrate. Shaping of an organic single crystal is demonstrated ferroelastically from linear to bent shape and from contracted to elongated shape. Rotation of sulfonate anions along with recombination and changes in lengths and angles in flexible hydrogen bonds of small water molecules helps ferroelastic mechanical twinning. Our findings demonstrate designability of mechanically twinnable organic crystals from the viewpoints of organic chemistry and crystal engineering based on hydrogen bonds.