Synthesis, structural, spectral and third-order nonlinear optical analysis of solution-grown 4-methylbenzylammonium oxalate hydrate: a novel organic crystal for laser applications

Organic single crystals of 4-methylbezyalammonium oxalate hydrate (4MLBAOX) have been successfully synthesized by adopting solvent evaporation method at room temperature. The structure of the grown crystal is solved. Cell parameters, space group, bond lengths and bond angles are determined. The 4-methylbenzylammonium cation, oxalic acid anion and the water molecule are linked by N–H…O, C–H…O, O–H…O hydrogen bonds. The existence of various stretching and bending vibrations of the functional groups have been analysed using FTIR and FT-Raman spectroscopy. The optical quality of the grown crystal has been analysed using UV–Vis-NIR spectral analysis. The transparency window is observed from 262 to 1100 nm for 4MLBAOX crystal. Nuclear magnetic resonance (¹H and ¹³C) spectroscopy establishes the molecular structure. The chemical shift of water of oxalic acid dihydrate reported at 8.2 ppm is shifted and observed at 4.89 ppm in 4MLBAOX. Similarly the NH₂ signal (1.42 ppm) is also shifted and observed at 7.353 ppm. The observed shifts in peak positions establishes the formation of the crystal. Z-scan analysis reveals the reverse saturable absorption and the self -focussing nature of the crystal. Hydrogen bonds present in the molecule improves the third-order nonlinear susceptibility value (χ³ = 2.9457 × 10⁻⁶ esu). The nonlinear refractive index (n₂) and absorption coefficient (β) have also been determined. The observed properties find applications in the generation of short laser pulses, optical limiting devices, frequency conversion processes and optoelectronic devices.