Calorimetric and Crystallographic Phase-Behavior Study of Selected 1-Butylpyridinium Ionic Liquids

Despite the growing popularity of ionic liquids (ILs) as attractive solvents with various interesting properties, lack low-uncertainty thermodynamic data persists for many these compounds. Even commonly available ILs, crucial parameters such melting temperatures and fusion enthalpies are often unknown or remain burdened significant uncertainties. Therefore, this study focuses on a thorough characterization phase behavior eight containing 1-butylpyridinium cation by means differential scanning calorimetry variable-temperature X-ray powder diffraction. In addition to studies, heat capacities ILs were determined using Tian-Calvet-type calorimeter. For compounds studied, presented first their kind. Four targeted exhibit polymorphic behavior, but its particular manifestations differ noticeably. The crystal-crystal transition in [BPy][NTf2] is irreversible barely noticeable both methods used, while [BPy][OTf] associated change entropy magnitude similar same compound. [BPy][PF6] exhibits textbook example lambda-shaped second-order between two crystalline phases, being rare phenomenon that more observed superfluids. Crystal structures polymorphs resolved may act solid foundation future theoretical computations.