Two quasi-spherical molecules [1,4-diazabicyclo(3.2.2)nonane]X (X = ClO4, ReO4) exhibit switchable phase transition, dielectric and second-harmonic-generation properties

Abstract

Often, the quasi-spherical molecule 1,4-diazabicyclo[2.2.2]octane (2.2.2-dabco) is chosen to prepare switchable materials with a high phase transition temperature. We wished to reduce molecular symmetry but maintain a quasi-spherical shape. Hence, a similar molecule, 1,4-diazabicyclo[3.2.2]nonane (3.2.2-dabcn), was used to react with equimolar amounts of HClO₄ or HReO₄ in aqueous solution. Two compounds [3.2.2-Hdabcn]X (X = ClO₄, 1; ReO₄, 2) with high phase-transition points at 418 K for 1 and 394.6 K and 419.2 K for 2, respectively, were isolated, in which one-dimensional cationic chains were connected by different types of hydrogen bonds. Differential scanning calorimetry and dielectric-permittivity measurements revealed that 1 and 2 showed switchable phase transition and dielectric anomalies. Compound 1 also showed a reversible second-harmonic-generation effect.