Pressure Effects on Crystallization, Polymorphism, and Solvation of 4,4′-Bipyridinium Perchlorate

Abstract

Pressure efficiently changes the crystallization preferences of three polymorphs and three solvates of 4,4′-bipyridinium perchlorate, [C10H9N2]+ClO4–. At ambient pressure a triclinic dihydrate [C10H9N2]+ClO4–·2H2O is formed of the solutions in water and in the water/methanol mixture, while the methanol solution in open vials yields concomitant monoclinic quarterhydrate 4([C10H9N2]+ClO4–)·H2O and triclinic anhydrate [C10H9N2]+ClO4–. At 0.30 GPa an orthorhombic anhydrate is formed, stable to 0.60 GPa, when it collapses into a monoclinic phase. The transition changes the conformation of cations from planar to twisted, differently than the analogue phase transition in [C10H9N2]+Br·H2O. Recrystallizations from the methanol solution above 0.55 GPa leads to methanol solvate [C10H9N2]+ClO4–·CH3OH. In the solvates, chains of the cations are aggregated through either NH+···N bonds (like in the neat polymorphs) or NH+···OH···N bonds, or both these bonds in one crystal. The pyridinium protons are disordered in all th...