ACr(C2O4)2(H2O)4 (A = Li or Na): two new coordination polymers of low dimensionality with different hydrogen‐bond networks

Single crystals of two new bimetallic oxalate compounds with the formula [ACr(C₂O₄)₂(H₂O)₄]_n (A = Li or Na), namely catena‐poly[[diaqualithium(I)]‐μ‐oxalato‐κ⁴O¹,O²:O^1′,O^2′‐[diaquachromium(III)]‐μ‐oxalato‐κ⁴O¹,O²:O^1′,O^2′], ( I ), and catena‐poly[[diaquasodium(I)]‐μ‐oxalato‐κ⁴O¹,O²:O^1′,O^2′‐[di‐aquachromium(III)]‐μ‐oxalato‐κ⁴O¹,O²:O^1′,O^2′], ( II ), have been synthesized, characterized and their crystal structures elucidated by X‐ray diffraction analysis and compared. The compounds crystallize in the monoclinic space group C2/m for ( I ) and in the triclinic space group P for ( II ); however, they have somewhat similar features. In the asymmetric unit of ( I ), the Li and Cr atoms both have space‐group‐imposed 2/m site symmetry, while only half of the oxalate ligand is present and two independent water molecules lie on the mirror plane. The water O atoms around the Li atom are disordered over two equivalent positions separated by 0.54 (4) Å. In the asymmetric unit of ( II ), the atoms of one C₂O₄^2? ligand and two independent water molecules are in general positions, and the Na and Cr atoms lie on an inversion centre. Taking into account the symmetry sites of both metallic elements, the unit cells may be described as pseudo‐face‐centred monoclinic for ( I ) and as pseudo‐centred triclinic for ( II ). Both crystal structures are comprised of one‐dimensional chains of alternating trans‐Cr(CO)₄(H₂O)₂ and trans‐A(CO)₄(H₂O)₂ units μ₂‐bridged by bis‐chelating oxalate ligands. The resulting linear chains are parallel to the [101] direction for ( I ) and to the [11] direction for ( II ). Within the two coordination polymers, strong hydrogen bonds result in tetrameric R₄⁴(12) synthons which link the metal chains, thus leading to two‐dimensaional supramolecular architectures. The two structures differ from each other with respect to the symmetry relations inside the ligand, the role of electrostatic forces in the crystal structure and the molecular interactions of the hydrogen‐bonded networks. Moreover, they exhibit the same UV–Vis pattern typical of a Cr^III centrosymmetric geometry, while the IR absorption shows some differences due to the oxalate‐ligand conformation. Polymers ( I ) and ( II ) are also distinguished by a different behaviours during the decomposition process, the precursor ( I ) leading to the oxide LiCrO₂, while the residues of ( II ) consist of a mixture of sodium carbonate and Cr^III oxide.     

Characterization of olive mill wastewater and gamma irradiation effects on some parameters of its composition

Journal of Radioanalytical and Nuclear Chemistry - Gamma irradiation was applied to olive mill wastewater and synthetic samples prepared from Gallic acid. The effects, generated on the...     

10-(4-Hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-3-methyl-1H,10H-pyrano[4,3-b] chromen-1-ones from a pseudo-multicomponent reaction and evaluation of their antioxidant activity

A series of novel 10-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-3-methyl-1H,10H-pyrano[4,3-b]chromen-1-ones were synthesized by a pseudo-three-component reaction of 4-hydroxy-6-methyl-2-oxo-2H-pyran-2-one (TAL) with 2-hydroxyarylaldehydes using different acids as catalysts and solvents. The approach relies on a regioselective cascade reaction involving two molar equiv of the TAL iteratively acting as active methylene in a Knoevenagel condensation and in a Michael addition. The antioxidant activity of the synthesized compounds were determined using the DPPH scavenging assay, being the results dependent on the nature and number of chromone substituents. The compound bearing an ortho-dihydroxy (catechol) moiety showed excellent activity at lower concentrations, while derivatives bearing alkoxy groups as substituents present pro-oxidant activity.     

Simultaneous Determination of Cobalt and Nickel Using Morpholinedithiocarbamate (MDTC) as Reagent by First and Second Derivative Spectrophotometry

A selective and sensitive derivative method has been proposed for the simultaneous determination of trace amounts of Co(II) and Ni(II) with morpholinedithiocarbamate (MDTC) in the presence of sodium lauryl sulphate (SLS). The molar absorption coefficients of the 1:2 complex of Co(II) and Ni(II) at 326 nm and 322 nm are 2.248 × 10⁴ and 2.505 × 10⁴ L mol^?1 cm^?1 for zero order. The analytical sensitivity for the second derivative of Co(II) and Ni(II) complexes are 0.0044 μg mL^?1 and 0.0060 μg mL^?1. The developed derivative procedure, using the zero‐crossing technique, has been successfully applied for the analysis of Co(II) and Ni(II) simultaneously in different alloy samples.     

Nouvelles synthèses de systèmes bicycliques hétéroaromatiques. I. Cycloaddition [4 + 2]π de la diméthyl-2,7 diméthylthio-3,5 triazépine-1,2,4

The cycloaddition of 3,5-dimethylthio-1,2,4-triazepine (1) to various dienophiles has been studied. 4-Phenyl-1,2,4-triazoline-3,5-dione, dimethyl acetylene dicarboxylate and meleic anhydride react with I to give the [4+2]π cycloadduct. The heterocyclic products were found to be formed via 1,3-sigmatropic rearrangement of this cycloadduct.     

Equilibrium diagram of KPO3–Y(PO3)3 system, chemical preparation and characterization of KY(PO3)4

Microdifferential thermal analysis (μ-DTA), X-ray diffraction (XRD) and infrared (IR) spectroscopy were used for the first time to investigate the liquidus and solidus relations in the KPO₃–Y(PO₃)₃ system. The only compound observed within the system was KY(PO₃)₄ melting incongruently at 1033 K. An eutectic appears at 13.5 mol% Y(PO₃)₃ at 935 K, the peritectic occurs at 1033 K and the phase transition for potassium polyphosphate KPO₃ was observed at 725 K. Three monoclinic allotropic phases of the single crystals were obtained. KY(PO₃)₄ polyphosphate has the P2₁ space group with lattice parameters: a=7.183(4) Å, b=8.351(6) Å, c=7.983(3) Å, β=91.75(3)° and Z=2 is isostructural with KNd(PO₃)₄. The second allotropic form of KY(PO₃)₄ belongs to the P2₁/n space group with lattice parameters: a=10.835(3) Å, b=9.003(2) Å, c=10.314(1) Å, β=106.09(7)° and Z=4 and is isostructural with TlNd(PO₃)₄. The IR absorption spectra of the two forms show a chain polyphosphates structure. The last modification of KYP₄O₁₂ crystallizes in the C2/c space group with lattice parameters: a=7.825(3) Å, b=12.537(4) Å, c=10.584(2) Å, β=110.22(7)° and Z=4 is isostructural with RbNdP₄O₁₂ and contains cyclic anions. The methods of chemical preparations, the determination of crystallographic data and IR spectra for these compounds are reported.     

Influence de certains ions inorganiques, de l'éthanol et du peroxyde d'hydrogène sur la photominéralisation du β-naphtol en présence de TiO2

TiO₂ photocatalytic mineralization of β-naphthol: influence of some inorganic ions, ethanol, and hydrogen peroxide. In this work, the photocatalytic oxidation of β-naphthol in aqueous suspensions of TiO₂ was investigated at room temperature, by following the formation of CO₂. The disappearance of β-naphthol fits a Langmuir-Hinshelwood kinetic model. The activation energy for the degradation reaction of β-naphthol is estimated at 10.2 kJ/mol. The effects of some additives such as ethanol, H₂O₂, and inorganic ions (Cl⁻, SO₄²⁻, HCO₃⁻, NO₃⁻, Fe³⁺, Cu^2+, and Cr³⁺) on the photomineralization of β-naphthol were examined. The inhibition of the anions for this reaction was in the order : NO₃⁻ < HCO₃⁻ < SO₄²⁻ < Cl⁻. This can be due to a partial blockage of catalyst active sites by these ions or their reaction with an oxidizing radical such as OH. The most photoactive systems for β-naphthol degradation were found in the presence of ferric ions, while the addition of Cr³⁺ strongly inhibited the photocatalytic decomposition of β-naphthol.     

Complexes of borane and N-heterocyclic carbenes: a new class of radical hydrogen atom donor

Calculations suggest that complexes of borane with N-heterocyclic carbenes (NHC) have B-H bond dissocation energies more then 20 kcal/mol less than free borane, diborane, borane-THF, and related complexes. Values are in the range of popular radical hydrogen atom donors like tin hydrides (70-80 kcal/mol). The resulting prediction that NHC borane complexes could be used as radical hydrogen atom donors was verified by radical deoxygenations of xanthates by using either AIBN or triethylborane as initiator.     

First total synthesis of 11-selena steroids

The first total synthesis of 11-selena steroids was achieved via an intramolecular Diels-Alder cycloaddition of o-quinodimethanes as the key step.     

Mathematical morphology for TOFD image analysis and automatic crack detection

The aim of this work is to automate the interpretation of ultrasonic images during the non-destructive testing (NDT) technique called time-of-flight diffraction (TOFD) to aid in decision making.