New Acid-base Crystalline Complexes with Second Harmonic Generation: Structural and Vibrational (Infrared Spectroscopic and Raman Spectroscopic) Characterisation of Nlo Materials

New crystalline complexes were obtained using strategy developed in recent years, strategy based on acid-base interactions. In this strategy, strong quadratic nonlinear coefficients of some organic compounds, are associated with the mechanical and thermal stability of mineral structures. Many crystals exhibit second harmonic generation of light. SHG efficiencies were measured using powder Kurtz-Perry method. Fortunately, for some complexes of melamine, fundamental condition for SHG, that is the lack of inversion center, was fulfilled. For centrosymmetric complexes of melamine, their potential ability to nonlinear optical response was suppressed by the action of inversion center. In each crystal, the intense hydrogen bond networks were found and characterized structurally and spectroscopically. In several crystals phase transitions were found.