Crystal growth, structural, optical, computational, and Z-scan analyses of imidazolium hydrogen oxalate crystal for nonlinear optical applications

Imidazolium hydrogen oxalate (IHO) single crystals were grown by the slow evaporation method. The title crystal crystallized in a monoclinic crystal structure with a centrosymmetric space group of P2₁/n. The ¹H NMR contains a peak at 4.90 ppm due to the presence of proton in oxalic acid. The O–H stretching vibration is noted at 3162 cm⁻¹ in FT-IR and in FT-Raman at 3172 cm⁻¹. The optical transparency and band gap were evaluated from the UV–Vis–NIR spectrum. The PL spectrum has a high violet emission band at 361 nm. TG/DTG study was used to find the thermal stability of the IHO crystal. Hirshfeld surface (HS) analysis revealed the molecular intermolecular interactions in the IHO molecule. The total polarizability (α) of the IHO molecule is 8.2652 × 10⁻²⁴ esu. The third-order nonlinear susceptibility [χ⁽³⁾] of the IHO crystal is determined to be 2.6422 × 10⁻⁹ esu.