Synthesis, characterization, and dielectric properties of 1,2-(propanediol)-3-methylimidazolium chloride, hydrogenosulfate, and dihydrogenophosphate ionic liquids

In this work, three 12-(propanediol)-3-methylimidazolium-based ionic liquids (ILs), each with a different anion-chloride ([Cl⁻]), hydrogen sulfate ([HSO₄⁻]), and dihydrogen phosphate ([H₂PO₄⁻])-were synthesized and thoroughly characterized. Structural integrity and purity were confirmed through ¹H and ¹³C nuclear magnetic resonance (NMR) and Fourier-transform infrared (FTIR) spectroscopy. Differential scanning calorimetry (DSC) analyses revealed distinct thermal behaviors, with each IL exhibiting unique melting and glass transition temperatures. The ionic conductivity was measured over a temperature range of 300K to 400K, showing that the choice of anion significantly influences conductivity. The IL with [H₂PO₄⁻] demonstrated the highest conductivity, attributed to its smaller ionic size and lower viscosity, followed by [Cl⁻], while [HSO₄⁻] displayed the lowest. Conductivity increased with rising temperature and frequency, reflecting greater ionic mobility in higher temperature and frequency conditions. These findings underscore the importance of anion selection in optimizing IL performance, particularly for applications requiring efficient ion transport, such as in electrochemical devices. The study highlights how molecular structure affects key properties like thermal stability and ionic transport, offering valuable insights for the design of ILs with tailored thermal and electrical characteristics. This research provides a foundational understanding of how the anionic component impacts the physicochemical properties of ILs, contributing to the development of new materials for energy storage, catalysis, and other advanced technologies requiring precise control over ionic conductivity and thermal properties.