Synthesis, structural, spectral and optical analysis of a novel semi-organic nonlinear optical crystal: Bis (4-methylbenzylammonium) hydrogen phosphate monohydrate

Bis (4-methylbenzylammonium) hydrogen phosphate monohydrate (4MLBAHP) single crystals were grown by reacting 4-methylbenzylamine (4MLBA) and orthophosphoric acid in 2:1 stoichiometric ratio using slow evaporation solution growth method. The structure of the grown crystal is solved and its space group is found to be \(P\overline{1 }\). The (C₈H₁₂N⁺)₂ cation, (HPO₄²⁻) anion and water molecules present in 4MLBAHP are joined through N–H…O and O–H…O bonds. The vibrations of 4MLBAHP functional groups were identified through FTIR and FT-Raman spectral techniques. The observed P-O, HPO₄²⁻ vibrations endorses the coordination of HPO₄²⁻ cation in the crystal structure. The lower cut off wavelength of 4MLBAHP was identified at 245 nm and the optical transmission bandwidth is from 245 to 1100 nm. The molecular structure is also established through NMR spectroscopy. In ¹H NMR, the protonation of NH₂ to NH₃⁺ causes the deshielding of NH₃⁺ protons and the corresponding signal is observed at 7.839 ppm.The third order nonlinear optical (NLO) susceptibility (χ³) is found to be 1.6949 × 10^–6 esu and this large value is attributed to the presence of hydrogen bonds in the molecular structure.