Luciano H. Chagas

Comparação estrutural entre amostras de materiais tipo hidrotalcita obtidas a partir de diferentes rotas de síntese

Three samples of hydrotalcite-like materials (HTC) were synthesized and their structural characteristics were compared with two HTCs obtained commercially. Thermal analyses, FT-IR, PXRD and textural analyses were used to investigate the structural differences between commercial and synthetic samples. Particularly, the memory effect was observed at temperature higher than 600 oC. The Rietveld refinements were obtained with expressive accuracy and the statistical parameters of goodness of fit are quite satisfactory. In conclusion, the procedures adopted in synthesis of HTC produced crystalline materials with high surface area materials.

Supramolecular structures of Mn2+, Co2+ and Zn2+ complexes containing 1,3-bis(4-pyridyl)propane and aminosalicylate anion

In this study, the synthesis, spectroscopic properties and crystal structures of three new supramolecular compounds named [Mn2(bpp)4(H2O)4](AS)4·H2O (1), [Co2(bpp)4(H2O)4](AS)4·H2O (2) and [Zn(bpp)(AS)2] (3), have been described, where bpp is 1,3-bis(4-pyridil)propane and AS− is aminosalicylate anion. By analysing the similarities between the X-ray powder diffraction results, it has been observed that compounds 1 and 2 are isomorphous, exhibiting an orthorhombic system with space group Pccn; for compound 3, another orthorhombic system was observed, with space group Aba2, which displays coordination between the Zn2+ metal ion and the aminosalicylate anion; this can be considered the first case in the literature involving the direct coordination to the metal ion. The vibrational spectra of compounds 1 and 2 are very similar. In the Raman spectra, the main bands are observed at ca. 1625 and 1020 cm− 1, referring to the − O–C = O and CC/CN stretching modes of AS− and bpp ligands, respectively.

Investigation of layered double hydroxides type ZnMgAl-carbonate and derivates.

Layered double hydroxides (LDHs) or hydrotalite-like compounds belong to a class of synthetic two-dimensional inorganic materials with lamellar structures, where the hydroxyl-hydrated compounds are formed by chemical substitution of divalent ion of the brucitelike octahedral layers by trivalent ions [1]. The LDH are represented by the general formula, Figure a , where M2+, M3+ are divalent and trivalent cation and Amis interlayer anion responsible by charge balancing, the range of divalent and trivalent ions (x) varies normally between 0.17 a 0.33. According Montanari and co-works [2] compounds type ZnAl-hydrotalcites (ZnAl-HT) have relevant industrial interest; however the scientific literature concerning this material as catalysts or catalyst precursor is scarce. Based on this fact, in the present communication we will present a studied on how the variation in percentage of Zinc in a ZnMgAl-HT catalyst precursor can influence the formation of mixed oxides after calcination. The ZnMgAl-HTs, Figure b , y=5, 10,15,20,25,50,75 and 100% were prepared by co-precipitation and urea method. Mg-Zn/Al mixed oxides were prepared from calcinations of hydrotalcites precursors at 500°C for 4 hours. The material synthesized were characterized by X-ray powder diffraction, the measurements were carried out in Bruker D8 DaVinci diffractometer, equipped with CuKα radiation , LynxEye linear Position Sensitive Detector, Ni-filter. Data was collect between 8 and 80° in 2θ with step size of 0.02° and the count time of 0.05 per step. Soller slit 2.5° of divergence and 0.2 mm primary slit were used. For the ZnMgAl-HT samples the measurements were performed at different temperatures, range 251200°C, heating rate 5°C/min. It was observed differences among XRD patterns for y greater than 25% of Zn in urea method at 500°C, and for co-precipitation method just for the substitution at 50 and 75% of Zn. These results suggested that the increase in Zn percentage change the structure of calcinated samples.

Structure Characterization of Materials by Association of the Raman Spectra and X-Ray Diffraction Data

Supramolecular chemistry, which can be described as the chemistry beyond the covalent bonds, has become a very interesting focus of investigation in the last years. The main purpose of this kind of studies is the strategic construction of specific arrangements, and the complete comprehension of the connection between structure and physical–chemical properties. However, in the solid state there are several weak interactions, as hydrogen bonds and -stacking, which can play a decisive role in orientation of the crystallization processes (Carlucci et al., 2003). Essentially, common features of all of the supramolecular systems are non-covalent interactions, which provide the clips linking the building blocks, leading to well organized superstructures (Yan et al., 2007). The term “Supramolecular chemistry” was introduced by Jean-Marie Lehn and it is defined as “the chemistry beyond the molecule”. While a covalent bond normally has a homolytic bond dissociation energy that ranges between 20 and 100 kcal mol-1, noncovalent interactions are generally weak and vary from less than 1 kcal mol-1 for van der Waals forces, through approximately 25 kcal mol-1 for hydrogen bonds, to 60 kcal mol-1 for Coulomb interactions (Hoeben et al., 2005). In this sense, the most important interactions in solid organic compounds are the hydrogen bonds. The kind and strength of these interactions added to the molecular arrangement are responsible for the crystal structure of these compounds. The change in production and/or storage conditions of solids may modify the hydrogen bonding design and the balance between them and van der Waals interactions. These modifications give rise several changes in the solid state, like phase transitions (Wang et al., 2009). Weak attractive forces are important in deciding the conformation of organic compounds and 3D structure of biomacromolecules. Among molecular interactions, the van der Waals force, electrostatic interactions and hydrogen bonds are the most important (Takahashi et al., 2010). Apart of hydrogen bonds, another type of interaction that plays an important role in the design of supramolecular materials is - interactions. Attractive non-bonded interactions between aromatic rings are seen in many areas of chemistry, and hence are of interest to all realms of chemistry. The strength as well as the causes of these interactions, however, varies. In water the stacking interaction between aromatic molecules is mainly caused by the

Thermal decomposition of ternary layered hydroxides

Multiferroics have engendered increasing interest because of their many potential applications for microor nano-electronic devices, magnetic storage elements and interesting fundamental physics. The term “multiferroic” means coexistence of ferroelectric and magnetic ordering in a single phase or multiphase material. However, the two ordering parameters are mutually exclusive because ferroelectricity and magnetism require different filling states of the d-shells of transition metal ions. Empty dshells mainly exist in ferroelectricity, while partially filled d-shells are required in magnetism. Therefore multiferroics are rare. It exists several different microscopic mechanisms which may cause multiferroic behaviour . One of the most interesting is when a spontaneous polarization exists in a spiral or cycloidal magnetic structure. Accordingly, one strategy to find new multiferroic materials is to look for magnetic systems with that kind of magnetic structures. The complex metal oxides Mn3TeO6 and Co3TeO6 have been prepared both as single crystals by chemical transport reaction and as polycrystalline powders by a solid state reaction route. The crystal structure and magnetic properties have been investigated using a combination of x-ray and neutron powder diffraction, electron microscopy, calorimetric and magnetic measurements. It has been shown that at room temperature Mn3TeO6 adopts a trigonal structure, space group R-3 (a= 8.8679(1)Å, c= 10.6727(2)Å) and Co3TeO6 the monoclinic spacegroup C 2/c (a=14.7830(2)A, b=8.8395(1)A, c=10.3426(2)A). A long-range magnetically ordered state has been identified through variable temperature neutron diffraction and magnetic susceptibility measurements. The magnetic structure for the two compounds is very different. Mn3TeO6 has an incommensurate helix structure while Co3TeO6 shows a complicated but commensurate spin structure.

Dipotassium tetra­aqua­bis­[3,5-bis­(dicyano­methyl­ene)cyclo­pentane-1,2,4-trionato(1−)-κN]cobaltate(II)

The title structure, K2[Co(C11N4O3)2(H2O)4], is isotypic with K2[Fe(C11N4O3)2(H2O)4]. The CoII atom is in a distorted octahedral CoN2O4 geometry, forming a dianionic mononuclear entity. Each dianionic unit is associated with two potassium cations and interacts with adjacent units through O—H⋯N and O—H⋯O hydrogen bonds.