Spectral and optical characterization of the new semi-organic crystal: 4-methylbenzylammonium chloride hemihydrate, to establish protonation and the effect of resultant hydrogen bonding

4-Methylbenzylammonium chloride hemihydrate (4MLBACH) single crystals were obtained by slowly evaporating the solvent. The characterization of the title crystal was first carried out and reported in this article. The crystal system and space group of the title crystal are identified as monoclinic and C2/c, respectively. The lattice parameter values were also calculated. Using Fourier transform infrared spectroscopy the protonation of 4-methylbenzylamine by hydrochloric acid and the formation of the crystal 4MLBACH were confirmed. The transmission window of the grown crystal is between 261 and 1100 nm. The protonation of the amine group is confirmed by nuclear magnetic resonance spectral analysis. Z-Scan analysis was carried out to determine the nonlinear optical parameters. It reveals that the nonlinear susceptibility ( $$\chi ³)$$ value is greater than some reported crystals. The title crystal exhibits saturable absorption and self-defocussing effects.