INFLUENCE OF MOLECULAR AND CRYSTAL STRUCTURE ON NONLINEAR OPTICAL PROPERTIES OF HYDRATED AND ANHYDROUS POTASSIUM L-2-NITRIMINO-1,3-DIAZEPANE-4-CARBOXYLATE CRYSTALS

The physical properties of crystals depend on their chemical composition and their molecular and crystal structure. The presence of donor amino groups (NH₂) and acceptor nitro groups (NO₂) in a molecule can increase the molecule’s non–linear optical (NLO) properties. L-nitroarginine, in a strong alkaline environment (MOH (M=Li,Na,K), crystallizes to form L-2-nitrimino-1,3-diazepane-4-carboxylic acid (L-NIDCA⋅H₂O and L-NIDCA). We found that the slow evaporation of a solution of L-nitroarganine and an alkali in equimolar
quantities leads to the formation of a metallic salt with L-2-nitrimino-1,3-diazepane-4-carboxylate anions
(K(L-NIDC)⋅H₂O, Na(-NIDC), L-NaNIDC, Li(L-NIDC); this salt shows strong NLO properties. This study also addressed the second-harmonic generation of L-KNIDC⋅H₂O and L-KNIDC crystals and how their crystal and molecular structure affects the NLO properties. The infrared and Raman spectra of K(L-NIDC)⋅H₂O and K(L-NIDC) crystals were studied with respect to these structural features. We found that the intensity of second-harmonic generation in K(L-NIDC) is 2.75 times higher than in the standard KDP crystal, while the intensity in K(L-NIDC)⋅H₂O is much lower.