Pressure-Induced Solvate Crystallization of 1,4-Diazabicyclo[2.2.2]octane Perchlorate with Methanol

Abstract

1,4-Diazabicyclo[2.2.2]octane perchlorate, [C6H13N2]+ClO4–, dabcoHClO4, the first NH+···N hydrogen-bonded ferroelectric, exhibits at least ten unsolvated polymorphs, depending on temperature and pressure. When crystallized from the methanol solution above 2 GPa, dabcoHClO4 crystallizes with two molecules of methanol to form solvate dabcoHClO4·2CH3OH. This solvate structure has been determined by single-crystal X-ray diffraction up to 3 GPa. High pressure transforms the H-bonding pattern and the hierarchy of different cohesion forces. The solvate formation is additionally favored by its molecular volume lower than the sum of the molar equivalents of unsolvated components.