A novel semi-organic single-crystal exhibiting third order optical nonlinearity was grown by the method of slow evaporation. Single crystal X-ray diffraction technique (XRD) was employed to confirm the crystal structure and powder XRD was used to determine the cell parameters. The sample was characterized using FT-IR, FT-Raman and UV–visible absorption and analysed with density functional theory (DFT) calculations. The detailed interpretation of the vibrational spectra has been carried out using normal coordinate analysis (NCA) through the scaled quantum mechanical force field methodology. The red shifting of NH stretching wavenumbers, both the observed and calculated, affirm that N–H……O type bonds are present in GuLG. The Natural Bond Orbital (NBO) analysis also points to a strong intermolecular N–H….O hydrogen bond. Thermal stability of the crystal was studied making use of the TG/DTA technique. The third-order nonlinearity studies, along with the optical limiting behaviour were investigated by Z-scan technique using diode-pumped Nd: YAG laser with 50 mW power at 532 nm.H © 2020 Elsevier B.V.