Evidence of second harmonic signals in poly[m2-L-alanine-m3-nitrato-sodium (I)] crystals

Poly[μ2 L- alanine- μ3- nitrato- sodium (I)] crystals have been grown by the slow evaporation at room temperature technique. The nominal size of the crystals obtained by the method was of 500 nm. The UV- vis spectrum shows a wide range where absorption is lacking around 532 nm, which is required in order to have incident radiation at a 1064 nm. This guarantees the possible use of the crystal in visible light applications. The transparent nature of the crystal in the visible and infrared regions within the transmission spectrum confirms the nonlinear optical properties of the crystal. Additionally, Fourier transform infrared spectroscopy displays its functional groups which correspond to the Poly[µ2-L-alanine-µ3-nitrate-sodium(I)], where the presence of nitrates in the lattice generally can be identified by their characteristic signature within the 1660-1625, 1300-1255, 870-833 and 763-690 cm-1 range. Single crystal diffraction was carried out in order to determine atomic structure and lattice parameter. The results showed that: a = 5.388(9) A, b = 9.315(15) A, c= 13.63(2) A, The structure of Poly[µ2-L-alanine-µ3-nitrate-sodium(I) shown by single crystal diffraction shows an  asymmetric unit consisting of one sodium and one nitrate ion and one L-alanine molecule. The coordination geometry around the sodium atom was trigonal bipyramidal, with three bidentate nitrate anions coordinating through their oxygen atoms and two L- alanine molecules, each coordinating through one carboxyl oxygen atom.   Key words:  L- alanine, second harmonic generation, nonlinear optical properties.