Crescimento e caracterização de cristais de cloreto, brometo e clorobrometo de bis-glicina

Abstract

Most of the research in the crystal growth area is directed in the search for crystals that are used as a reliable frequency converter, And for this it is necessary good NLO coefficient, wide range of transparency in the visible spectrum region, high thermal stability, high Damage threshold, High mechanical strength, ease of growth and low cost of production. The semiorganic crystals aim to combine properties of inorganic materials and purely organic compounds in order to potentiate their properties for optoelectronic applications. Due to its amphoteric behavior, glycine can react with both cations and anions forming numerous complexes with metal ions by means of ionic bonding or even forming semiorganic salts with ions of the series of halogens that stabilize by means of hydrogen bonds. This leads glycine to be the most extensively studied amino acid. This work aims at the synthesis and characterization of crystals of bis-glycine hydrobromide (BGHBr), bis-glycine hydrochloride (BGHCl) and the unpublished bis-glycine chlorobromide crystal (BGHClBr) promoted by the mixture of the growth solutions of the Crystals previously mentioned in the equimolar proportion. The three crystals were grown by the solvent evaporation technique, which were colleted after an average period of 7 to 8 weeks and characterized by X-ray fluorescence, Xray diffraction techniques in conjunction with the refinement of structures by the Rietveld method, FTIR, Raman spectroscopy, differential scanning calorimetry, of XRD as a function of temperature. By means of the XRF analysis it was possible to confirm that ions Cland Brentered the crystal structure of BGHClBr in almost equal concentrations. The XRD analyzes at room temperature in conjunction with the refinement of structures by the Rietveld Method have shown that the synthesized crystals are structural isomorphs having orthorhombic structure (spatial group P212121). The network parameters of the BGHBr and BGHCl samples are in accordance with what has been reported in the literature, presenting a difference of less than 1% and the crystal parameters of BGHClBr have values intermediate to those of the other two crystals, indicating the development of a new crystal. Assignments for the bands presented in the FTIR and Raman spectrum confirmed the existence of two different glycine molecules present in the crystals. One is in the dipole form (NH3 +CH2COO- ) and the other in cationic form (NH3 +CH2COOH). In addition, the similarity between the three spectra can be noted indicating that the three crystals have the same functional groups. The Raman spectra show that the internal modes were practically the same in some regions, indicating the isomorphism between the three samples and that the network modes are different for the three crystals, and in this way these results are in agreement with the XRD analyzes confirming the development of the new material. The DSC curves indicate that the crystal of BGHCl is more stable with melting temperature at approximately 189 °C, the other two, BGHBr and BGHClBr, exhibited the same event at the temperature of approximately 172 °C and 177 °C, respectively. The XRD analyzes in function of temperature indicate the formation and a new phase for BGHBr crystal at about 160 °C. As the crystals of BGHCl and BGHBr already have their efficiency proven in the process of generation of the second harmonic and due to the thermal stability observed for the three crystals, and considering that new crystal developed in this work is structural isomorph of these semiorganic salts, these materials Are promising in the application in non-linear optical devices.