Non-bonded interactions and its contribution to the NLO activity of Glycine Sodium Nitrate – A vibrational approach

Vibrational spectral analysis of the novel nonlinear optical (NLO) material, Glycine Sodium Nitrate (GSN) is carried out using NIR FT-Raman and FT-IR spectroscopy, supported by Density Functional Theoretical (DFT) computations to derive equilibrium geometry, vibrational wave numbers and first hyperpolarizability. The reasonable NLO efficiency, predicted for the first time in this novel compound, has been confirmed by Kurtz–Perry powder SHG experiments. The influence of Twisted Intramolecular Charge Transfer (TICT) caused by the strong ionic ground state hydrogen bonding between charged species making GSN crystal to have the non-centrosymmetric structure has been discussed. The shortening of CH bond lengths, blue-shifting of the stretching frequencies and intensity variation indicating the existence of ‘blue-shift or improper’ CH⋯O hydrogen bonding. The intense low wavenumber H-bond Raman vibrations due to electron–phonon coupling and non-bonded interactions in making the molecule NLO active have been analyzed based on the vibrational spectral features. The Natural Bond Orbital (NBO) analysis confirms the occurrence of a strong intra- and intermolecular NH⋯O and CH⋯O hydrogen bonds.