Structural phase transitions and dielectric transitions in a 1,4-diazabicyclo[2.2.2]octane (dabco) based organic crystal

Abstract

1,4-Diazabicyclo[2.2.2]octane (dabco) based organic crystal [(Hdabco)(H2O)](PF6) (1) was synthesized and characterized. Its structure is featured by wavy-like one-dimensional supramolecular hydrogen bond chains built from the [(Hdabco)(H2O)] units from end to end. Compound 1 undergoes two reversible phase transitions at 226/268 K and 178/181 K, respectively. The disorder-order transition of water molecule in the hydrogen bond chain induces the phase transition at 226 K while the twisting of the [Hdabco]+ cation and displacements of the PF6− anion and H2O molecules trigger the phase transition at 178 K. Dielectric transitions are thus triggered in the crystal.