Nonlinear optical materials have been investigated recently due to their potential technological applications in information storage and communications. In this context, semi-organic crystals can effectively combine the desired nonlinear optical properties of amino acids with the promising mechanical and thermal properties of inorganic materials. In this work, we have synthesized and characterized a semi-organic crystal of the amino acid l-histidine and hydrofluoric acid and investigated the chemical interactions between the organic and inorganic moieties. The crystal of l-histidine bis(fluoride) has been produced by slow solvent evaporation and characterized by X-ray diffraction (XRD) crystallography and thermogravimetric and differential thermal analyses. The XRD conducted using the Rietveld method shows that the unit cell is orthorhombic with the P21212 space group and contains four l-histidine bis(fluoride) units. Both differential thermal analysis and temperature-dependent XRD show that the crystals are thermally stable up to 191°C and do not undergo phase transition. The computational Hirshfeld surface analysis of the crystal structure reveals the main intermolecular interactions. Density functional theory has been employed to calculate the ionic interaction energy and electrostatic potential maps and confirm the spontaneity of ionic association at 191°C. The combined experimental and computational results show that the thermal stability of the semi-organic l-histidine bis(fluoride) crystal makes it suitable for nonlinear optical applications in optical sensing and communication systems.
Graphical abstract
RESUMO A síntese de cristais semiorgânicos formados por aminoácidos e metais nos últimos anos tem ganhado maior atenção devido às propriedades estruturais e vibracionais promissoras destas moléculas. Neste âmbito, este trabalho visou à síntese de um monocristal de L-Treonina complexado com o íon Cu2+ pelo método de evaporação lenta do solvente, bem como o estudo das propriedades estruturais, vibracional e térmica. O material foi obtido após 30 dias em pH 5.8. Verificou-se por meio da Difração de raios X que o cristal sintetizado possui estrutura monoclínica com grupo espacial P21. A análise por termogravimetria mostrou que o material é estável ate 50 °C, sofrendo uma transformação de fase por meio da perda das moléculas de água na célula unitária. Em 180 °C a DRX em conjunto com o método de Le Bail mostrou que o material adquire uma nova conformação estrutural, permanecendo em um sistema monoclínico e transitando para o grupo de simetria P121.
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