Anna Olejniczak, Michalina Anioła, Marek Szafrański, Armand Budzianowski and Andrzej Katrusiak
REPRINTED WITH PERMISSION FROM CRYST. GROWTH DES., 2013, 13 (7), PP 2872–2879 DOI: 10.1021/CG400276C. COPYRIGHT (2013) AMERICAN CHEMICAL SOCIETY.
Exceptionally rich diagram of ten phases, I–X, has been revealed for ferroelectric 1,4-diazabicyclo[2.2.2]octane perchlorate, [C6H13N2]+ClO4–, dabcoHClO4. Pressure- and temperature-induced transformations of this NH+···N hydrogen bonded structure have been characterized by single-crystal X-ray diffraction, calorimetric, and dielectric measurements. At high pressure the single crystals were in situ grown in a diamond-anvil cell at isochoric conditions. There are nine phases of dabcoHClO4 between 400 and 11K at ambient pressure, whereas phase X is formed at 1.5GPa and 296K. Tetragonal phase I space group P4/mmm transforms to orthorhombic phases II (Pm21n), III (Pc21n), IV (Pc2a), and V (orthorhombic-modulated) on decreasing temperature. Phase II is stable up to 0.22GPa, at 0.6GPa phase III is formed, and above 1.50GPa a new phase X (Pc21a) has been obtained. At normal conditions dabcoHClO4 is isostructural with the ferroelectric crystal of dabcoHBF4; however, their phase diagrams are very different. Above 1.8GPa dabcoHClO4 cocrystallizes with solvate molecules.