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
RESUMOA hidroxiapatita é um fosfato de cálcio considerada como biomaterial utilizada em restaurações ósseas, uma vez que apresenta características semelhantes à fase mineral do tecido ósseo. Por possuir diversos métodos de obtenção, a síntese do pó de hidroxiapatita tem estimulado interesse de pesquisas acadêmicas e indústrias, pois as condições de síntese e dos reagentes influenciam na estrutura, morfologia e aplicação do composto final desejado. Este trabalho propende realizar um estudo comparativo sobre síntese do pó de hidroxiapatita utilizando reagentes iguais, por dois métodos diferentes: mecanoquímica e calcinação. A síntese da hidroxiapatita foi realizada pela reação de estado sólido utilizando como precursores, o hidróxido de cálcio e o fosfato monoácido de cálcio em quantidades estequiométricas. As caracterizações foram realizadas por difração de raios X, espectroscopia Raman, microscopia eletrônica de varredura, espectroscopia de energia dispersiva, densidade, porosidade e microdureza Vickers. Os difratogramas de raios X apresentaram única fase para o método mecanoquímico e mais de uma fase para o método de calcinação, as fases foram confirmadas após refinamento pelo método de Rietveld e o tamanho médio do cristalito foi calculado pela equação de Scherrer. A espectroscopia Raman evidenciou bandas dos modos vibracionais da hidroxiapatita. As micrografias caracterizaram as diferenças morfológicas ocorridas nas amostras devido a diferentes métodos de síntese e a espectroscopia de energia dispersiva indicou as razões cálcio/fósforo das amostras, classificando-a como cerâmica à base de fosfato de cálcio. Medidas de densidades e porosidades das amostras foram realizadas, utilizando o método do picnômetro, baseado no princípio de Arquimedes. Os valores encontrados foram satisfatórios, pois estão próximos a valores teóricos encontrados na literatura. Medidas de microdureza Vickers foram obtidas nas amostras, com o intuito de averiguar suas propriedades mecânicas. Os métodos empregados se mostraram eficazes na produção de pós da hidroxiapatita.Palavras-chave: hidroxiapatita, mecanoquímica, calcinação. ABSTRACTHydroxyapatite is a calcium phosphate considered a biomaterial used in bone restorations, since it has characteristics similar to the mineral phase of bone tissue. Due to its many methods of production, the synthesis of hydroxyapatite powder has stimulated interest of academic research and industries, as the conditions of synthesis and reagents influence the structure, morphology and application of the desired final compound. This work aims to perform a comparative study on hydroxyapatite powder synthesis using equal reagents by two different methods: mechanochemical and calcination. The synthesis of hydroxyapatite was performed by solid state reaction using as precursors, calcium hydroxide and calcium monoacid phosphate in stoichiometric quantities. The characterizations were performed by X-ray diffraction, Raman spectroscopy, scanning
Tutton salts have been extensively explored in recent decades due to their attractive physical and chemical properties, which make them potential candidates for thermochemical heat storage systems and optical technologies. In this paper, a series of new mixed Tutton salts with the chemical formula (NH4)2Mn1–xZnx(SO4)2(H2O)6 is reported. Crystals are successfully grown by the solvent slow evaporation method and characterized by powder X-ray diffraction (PXRD) with Rietveld refinement. In particular, the crystal structure of the mixed (NH4)2Mn0.5Zn0.5(SO4)2(H2O)6 crystal is solved through PRXD data using the DICVOL06 algorithm for diffraction pattern indexing and the Le Bail method for lattice parameter and spatial group determination. The structure is refined using the Rietveld method implemented in TOPAS® and reported in the Cambridge Structural Database file number 2104098. Moreover, a computational study using Hirshfeld surface and crystal void analyses is conducted to identify and quantify the intermolecular interactions in the crystal structure as well as to determine the amount of free space in the unit cell. Furthermore, 2D-fingerprint plots are generated to evaluate the main intermolecular contacts that stabilize the crystal lattice. Density functional theory is employed to calculate the structural, thermodynamic, and electronic properties of the coordination [Zn(H2O)6]2+ and [Mn(H2O)6]2+ complexes present in the salts. Molecular orbitals, bond lengths, and the Jahn–Teller effect are also discussed. The findings suggest that in Mn-Zn salts several properties dependent on the electronic structure can be tuned up by modifying the chemical composition.
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