Toward Understanding the Origin of Structural Phase Transition in Guanidinium Pyridinium 1,5-Naphthalenedisulfonate

A phase transition compound 9PY was
screened from a series of organic
salts (Cat)·G·NDS, where the Cat is protonated amine or N-containing heterocycle (Cat = methylammonium, 1MA; ethylammonium,
2EA; propylammonium, 3PA; dimethylammonium, 4DMA; isopropylammonium,
5iPA; tert-butylammonium, 6tBA; imidazolium, 7IM;
pyrazolium, 8PZ; pyridinium, 9PY; 2-methylimidazolium, 10MIM; 2-ethylimidazolium,
11EIM; (R,S)-3-methylpiperidium,
12MP), the G is guanidinium, and the NDS is 1,5-naphthalenedisulfonate.
Detailed crystal structural analysis of 9PY shows the competing hydrogen-bonding
interactions among the pyridinium and sulfonates are the driving force
for the structural phase transition at 211 K.