Synthesis, structural characterization and high pressure phase transitions of monolithium hydronium sulfate

A three dimensional lithium hydronium sulfate LiSO4·H3O [1], [space group Pna21a=8.7785(12) Å, b=9.1297(12) Å, c=5.2799(7) Å, V=423.16(10) Å3] was synthesized via solvothermal methods using 1,5-naphthalenedisulfonic acid (1,5-NSA) as the source of sulfate ions. The structure of [1], determined by single crystal X-ray diffraction techniques, consists of corner sharing LiO4 and SO4 tetrahedra, forming an anionic 3-D open framework that is charge balanced by hydronium ions positioned within channels running along [001] and forming strong H-bonding with the framework oxygen atoms. Compound [1] undergoes two reversible phase transitions, involving reorientation of SO42− ions at pressures of approximately 2.5 and 5 GPa at room temperature, as evident from characteristic discontinuous frequency drops in the ν1 mode of the Raman spectra. Additionally, compound [1] forms dense β-lithium sulfate at 300 °C, as evident from temperature dependent powder XRD and combined reversible TGA-DSC experiments.

Graphical abstractLeft: View of corner-shared LiO4 and SO4 tetrahedra along [001] direction with hydronium ions situated in the channels. Right: (a) Photograph of the loaded DAC (b) Ambient pressure Raman spectrum of compound [1] (c) Evolution of the ν1 mode with the increasing and decreasing pressure indicating transitions to high-pressure phases at ∼2.5 (red curves) and ∼5 GPa (blue curves) and at ∼3.5 GPa upon decompression.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► A 3-D lithium hydronium sulfate is synthesized by solvothermal methods. ► Two high pressure phase transition occurs due to rotation of sulfate groups. ► The framework undergoes a high temperature structural transformation, to form β-Li2SO4 phase.