2,2′,6,6′-Tetrachloro-4,4′-propane-2,2-diyldiphenol, 2,2′,6-tribromo-4,4′-propane-2,2-diyldiphenol and 2,2′,6,6′-tetrabromo-4,4′-propane-2,2-diyldiphenol

Three flame retardants with very similar molecular structures showing three different packing patterns have been studied. The crystal structure of 2,2′,6,6′-tetrachloro-4,4′-propane-2,2-diyldiphenol, C₁₅H₁₂Cl₄O₂, can be described as a packing of sheets. The packing shows a very short intermolecular Cl⋯Cl contact distance of 3.094 (2) Å between pairs of mol­ecules inside each sheet. The crystal structure of 2,2′,6-tribromo-4,4′-propane-2,2-diyldiphenol, C₁₅H₁₃Br₃O₂, can be described as a packing of doubly stranded helical square tubes. These square helices are interconnected through Br⋯Br contacts between different helices. Finally, a previously known structure, 2,2′,6,6′-tetrabromo-4,4′-propane-2,2-diyldiphenol [Simonov, Cheban, Rotaru & Bels'skii (1986). Kristallografiya, 31 , 397–399], C₁₅H₁₂Br₄O₂, which is the most commonly used flame retardant and which has twofold rotational symmetry, has been refined in the correct absolute configuration. The structure shows large differences from the chloro analogue with regard to packing, van der Waals distances and hydrogen-bond distances.     

Nachweis und Bestimmung des Mangans sowie seine Trennung von anderen Elementen

Ohne Zusammenfassung     

Effect of particle size on carburization of Fe-Co alloy catalysts

Bimetallic Fe-Co alloy catalysts supported on silica have been studied by use of combined Mössbauer absorption and emisson spectroscopy. Effects of carburization on samples with different particle size are discussed.     

Optical properties of TiN1-x single crystals

The reflectance spectra of TiN_1–x single crystals were measured at room temperature. The chemical composition of the crystals was varied between TiN_1–0.00 and TiN_1–0.43. The experimental data are analyzed on the basis of a Lorentz-Drude model in order to determine the influence of nitrogen vacancies on the electrical conductivity, on the carrier concentration, and on the collision time.     

An interpenetrating primitive cubic net formed by hydrogen bonds and coordination bonds in catena‐poly[[bis(methanol‐κO)bis(thiocyanato‐κN)iron(II)]‐μ‐1,2‐bis(4‐pyridylmethylene)hydrazine‐κ2N:N′]

In the title compound, [Fe(NCS)₂(C₁₂H₁₀N₄)(CH₄O)₂]_n, at 153 (2) K, the Fe atom is located on an inversion centre, as is the centre of the N—N bond in the ligand molecule. The structure contains a one‐dimensional coordination polymer with an Fe...Fe distance of 15.866 (7) Å and can be described as two interpenetrating six‐connected primitive cubic (pcu) three‐dimensional networks when additional intermolecular O—H...S hydrogen bonds are taken into account. The compound is not isostructural with the corresponding Mn^II compound as they differ in the rotation around the M—O bond by 90°, giving rise to completely different hydrogen‐bond patterns. This study demonstrates the impact of conformational differences on the final supramolecular arrangement.     

Molecular modeling of interfaces between cellulose crystals and surrounding molecules: Effects of caprolactone surface grafting

A technical problem in cellulosic nanocomposite materials is the weak interaction between hydrophilic cellulose and hydrophobic polymer matrices. One approach to solve this difficulty is to chemically graft monomers of the matrix polymer onto the cellulose surface. An important question is to understand the effect such surface modification has on the interfacial properties. Semi-empirical approaches to estimate work of adhesion based on surface energies do not provide information on specific molecular interactions. Details about these interactions were obtained using molecular dynamics (MD) simulation. Cellulose interfaces with water and caprolactone medium were modeled with different amounts of grafted caprolactone. The modification lead to an increased work of adhesion between the surface and its surrounding medium. Furthermore, the MD simulations showed that the interaction between cellulose, both modified and non-modified, and surrounding medium is dominated by Coulomb interactions, predominantly as hydrogen bonds.