Conformational Transformations of (C12H25NH3(+))(Pyridinesulfonate) in the Solid State.

The phase-transition behaviors, crystal structures, and dielectric properties of four kinds of simple 1:1 organic salts of (C12H25NH3(+))(benzenesulfonate) and (C12 H25NH3(+))(pyridine sulfonates) were examined from the viewpoint of intermolecular hydrogen-bonding interactions and dynamic conformational transformation in molecular assemblies. Crystals of (C12H25NH3(+))(benzenesulfonate) and (C12H25NH3(+))(3-pyridinesulfonate) were isostructural and solid-solid and solid-liquid-crystal smectic A (SmA) phase transitions were observed. These two crystals formed rodlike cation-anion assemblies. However, the two salts, (C12H25NH3(+))(2-pyridinesulfonate) and (C12H25NH3(+))(4-pyridinesulfonate), formed largely bent L-shaped cation-anion conformations. Interesting conformational transformations from rodlike to L-shaped assemblies were observed in (C12H25NH3(+))(2-pyridinesulfonate) and (C12H25NH3(+))(3-pyridinesulfonate).

Successive Phase Transition, Dielectric Ordering, and Liquid Crystalline Behavior of Simple (Laurylammonium)(Phenyl Phosphates) Salts.

Successive phase transitions of three kinds of simple 1:1 organic salts of laurylammonium (LA)-phenyl (3-pyridyl) phosphate derivative were examined in terms of thermal properties, single crystal X-ray structural analyses, powder X-ray diffractions, and dielectric responses, where the phosphate anion was chemically modified from phenylphosphate (1) and 3-pyridylphosphate (2) to m-fluorophosphate (3). All 1:1 simple organic salts showed the successive solid-solid and solid-smectic A (SmA) phase transition with high thermal stability. Isostructural alternate cation-anion layer was observed in LA-1 and LA-2, and the packing structure of LA-3 was different from those of the former salts. The L-shaped cation-anion conformation in the molecular assemblies was transformed to the rod-like conformation through the phase transition to SmA phase, where both conformations coexisted in the intermediate solid phase of LA-2 and LA-3. The DSC, PXRD, and dielectric responses of LA-2 showed the antiferroelectric-paraelectric phase transition couple with the flip-flop motion of 3-pyridyl ring along the long axis of the molecule. On the contrary, such molecular motion of the phenyl ring did not show the dielectric phase transition due to no dipole change during molecular rotation of phenyl ring. The motional freedom of m-fluorophenyl ring in LA-3 was completely suppressed by the steric hindrance from the neighboring anions in the absence of dielectric ordering.