Theoretical studies of electronic and crystal structure properties of anhydrous mercury oxalate

The results of theoretical analysis of the crystal structure and bonding in relation to thermal decomposition process in anhydrous mercury oxalate are presented. The methods used Bader’s Quantum Theory of Atoms in Molecules formalism with bond order model (by Cioslowski and Mixon), applied to electron density obtained from ab initio calculations carried out with FP-LAPW Wien2k package (Full Potential Linearized Augmented Plane Wave Method) and Brown’s Bond Valence Model are described. The analysis of the obtained results shows that most probably the thermal decomposition process of mercury oxalate should lead to metal and CO₂ as products (as it is experimentally observed). Presented results (as well as the results of our similar calculations carried out previously for zinc, cadmium silver, cobalt and calcium oxalates) allow us to state that such methods (topological and structural), used simultaneously in analysis of the crystal structure and bonding properties, provide us with the additional insight into given compound’s behavior during thermal decomposition process. As a result, these methods can be considered as valuable supporting tool in the analysis of thermal decomposition process in given compound.     

Isomerization of cyclobutane ligands in the solid state and solution

Cyclobutane compounds are a class of compounds that can be conveniently synthesized in the solid state by employing crystal engineering principles. The rctt-isomer (or the syn-dimer) is the most common form of any cyclobutene compound that is obtained in the solid state by the photochemical [2 + 2] cycloaddition reactions. However, these rctt-isomers can be converted to other less accessible forms, under some special conditions. Isomerization of cyclobutane compounds thus plays an important role in synthetic chemistry. Such isomerization of cyclobutane compounds have been reported in organic salts, metal complexes, coordination polymers and metal-organic frameworks. In this review, these fascinating examples of isomerization that occur both in the solid state and solution phase have been discussed.     

An ultra-low hydrolysis sol-gel route for titanosilicate xerogels and their characterization

In this work TiO₂-SiO₂ xerogels were prepared through an ultra low hydrolysis method using titanium and silicon alkoxide. The samples were heat treated to 500°C. The xerogels were characterized using TGA/DTA, FTIR, XRD and TEM. The samples showed the formation of Si–O–Ti bridges by its characteristic vibration within 925–960 cm⁻¹ range. Si–O–Si bond angles were calculated using the central force network model. The TiO₂ in all the samples crystallized on heat treatment to 500°C. The crystallite size calculated using the Scherer formula from the XRD was verified from the Transmission Electron Micrograph. Samples heat treated to 350°C remained amorphous and hence could be used as hosts for biomaterials and organic optical materials.     

Crystal structure, electronic structure, and bonding properties of anhydrous nickel oxalate

The results of crystal structure determination and theoretical analysis of electronic structure and bonding properties in relation to thermal decomposition process in anhydrous nickel oxalate are presented. The details of the methods used in this analysis i.e., the Bader’s quantum theory of atoms in molecules and bond order models (as defined by Pauling, Bader, Cioslowski and Mixon—modified by Howard and Lamarche), applied to topological properties of the electron density, obtained from ab initio calculations carried out by Wien2k FP-LAPW package (full potential linearized augmented plane wave method), as well as Brown’s bond valence model (bond valences and strengths, and bond and crystal strains, calculated from experimental crystal structure data) are described. Nickel oxalate dihydrate was prepared by precipitation from water solutions of nickel nitrate (V) with oxalic acid at about 60 °C. The crystalline powder was filtered, washed, and dried at 80 °C on air. Anhydrous nickel oxalate sample was measured by XRD method applying Philips X’Pert Pro MD diffractometer equipped with MRI high temperature cell. Structural as well as qualitative and quantitative phase analyses were made by Phillips X’Pert HighScore Plus version 2.1 software with implemented full-pattern fit by means of Rietveld method. The detailed analysis of the obtained results shows that anhydrous nickel oxalate has monoclinic crystal structure (P2₁/c, sg 14), the carbon–carbon bond is the weakest one, and the process of thermal decomposition of this structure should begin with the breaking of this particular bond followed by nickel-oxygen bonds, which will lead to metallic nickel and carbon dioxide as final products, in agreement with the experiment. These results, supported by our earlier ones show clearly that such methods (topological and structural), when used simultaneously in analysis of the crystal structure and bonding properties, provide us with the additional insight into the behavior of given compound during thermal decomposition process and thus allow predicting and explaining of its most probable pathway.     

Dependence of flow behaviour on carbon black distribution in polyblend systems

The flow behaviour of four blend systems was determined at four shear rates and three processing temperatures using an extrusion rheometer. The blends were based on natural rubber/polybutadiene elastomers and were prepared using various mixing sequences with the carbon black being added in different ways.The degree of die swelling was found to depend on the blending technique, the processing temperature and the extrusion rate. A theoretical model was used to calculate the stored elastic energy, shear modulus and relaxation time. Melt fracture was observed when the carbon black was premixed in just one component of the blend.     

Effect of three-body forces on the lattice dynamics of noble metals

A simple method to generate an effective electron-ion interaction pseudopotential from the energy wave number characteristic obtained by first principles calculations has been suggested. This effective potential has been used, in third order perturbation, to study the effect of three-body forces on the lattice dynamics of noble metals. It is found that three-body forces, in these metals, do play an important role. The inclusion of such three-body forces appreciably improves the agreement between the experimental and theoretical phonon dispersion curves.     

Methane sensor based on palladium/MWNT nanocomposites

Methane gas sensor was fabricated based on electrocatalytic properties of the Pd/MWNT nanocomposites on indium tin oxide (ITO)glass substrates.A linear response for methane was obtained in the range of 0-16%(v/v)with a detection limit of 0.167%(v/ v)and R.S.D.of 4.1%.After 100 times sensing or stable stored more than 12 months in atmosphere,unconspicuous measurable decrease was observed.The response time was less than 60s at room temperature and ambient pressure.Some common potential interferents in samp...     

Citrinal A,a novel tricyclic derivative of citrinin,from an algicolous fungus Penicillium sp.i-1-1

Citrinal A(1),a novel tricyclic compound with a rare tetrahydro-2H-benzofuro[7-b][1,4]dioxin-9(3H)-one skeleton,along with two known related compounds,citrinin(2) and 2,3,4-trimethyl-5,7-dihydroxy-2,3-dihydrobenzofuran(3) were isolated from an algicolous fungus Penicillium sp.i-1-1.The structure and stereochemistry of 1 were determined by comprehensive spectral and biogenic analysis.Its cytotoxic effects on the A-549 and HL-60 cell lines were evaluated.     

FeCl_3 catalyzed diarylmethanes formations

Under mild condition,using FeCl3 as catalyst,a series of functionalized diarylmethanes were prepared efficiently from the reactions of arenes with paraformaldehyde.This catalytic system is not sensitive to air and moisture.