Reversible Phase Transition of 1,4-Diazoniabicyclo[2.2.2]octane-1-acetate-4-acetic
Acid Chloride Trihydrate
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Abstract
1,4-Diazoniabicyclo[2.2.2]octane-1-acetate-4-acetic
acid forms a complex (<b>1</b>) with chloride ion and water
molecule in the ratio 1:1:3. Differential scanning calorimetry (DSC)
measurement shows a pair of reversible peaks at 210.7 K (heating)
and 180.3 K (cooling) with a large heat hysteresis about 30.4 K, indicating
this compound undergoes a reversible structural phase transition.
Dielectric measurement further confirms the phase transition. The
DSC and dielectric measurements results of its deuterated compound
(<b>2</b>) exhibit obvious change compared to those of <b>1</b>. The crystal structures of these two compounds, determined
at 153 and 298 K, are all monoclinic in <i>P</i>2<sub>1</sub>/<i>n</i>, suggesting the phase transition is isosymmetric.
Structural analysis reveals that the changes of the relative location
of water molecules and chloride ions affect the formation of different
modes of hydrogen-bonded anionic chains, leading to the reversible
structural phase transition