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

Abstract

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 equimolarquantities 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.