Poly[diaquadi‐μ6‐oxalato‐μ5‐oxalato‐chromium(III)rubidium(I)]: a new supramolecular isomer

The title compound, [CrRb(C₂O₄)₂(H₂O)₂]_n, obtained under hydrothermal conditions and investigated structurally at 100 K, is a three‐dimensional supramolecular isomer of the layered structure compound studied at room temperature. This novel polymer is built up from crosslinked heterobimetallic units. The linkage of alternating edge‐ and vertex‐shared RbO₇(H₂O)₂ and CrO₄(H₂O)₂ polyhedra running along three different directions gives a dense packing. The two independent ligands display two η⁴‐chelation modes and two conventional carboxylate bridges. However, the pentadentate ligand connects the Cr^III and Rb^I ions through one O‐atom bridge, while the hexadentate ligand exhibits an additional η³‐chelation and two O‐atom bridges. Each coordinated water molecule forms an O‐atom bridge between the two metals. Moreover, in the absence of protonated ligands, these water molecules act as donors through their four H atoms in strong‐to‐weak hydrogen bonds. This results in zigzag chains of alternating oxalate and aqua ligands parallel to the twofold screw axis. The six double oxalates known to date containing an alkali and Cr^III all present layered two‐dimensional structures. In the series, this supramolecular isomer is the first three‐dimensional framework.     

Stabilization of Th ions into mixed-valence thorium fluoride

The unusual oxidation state +3 of the thorium has been stabilized into a lithium containing non-stoichiometric mixed-valence (III/IV) thorium fluorinated phase with formula Li_2+xTh₁₂F₅₀ (0<x<1.8). This phase is closely related to the Li_5.5Ce₁₂F₅₀ one, the structure of which has been determined from the combined single-crystal X-ray diffraction and high resolution synchrotron powder diffraction. In these phases, the Li⁺ ions can be divided into two groups and are located either in locked positions or in open channels of the three dimensional framework. The amount of Li⁺ ions in open channels can be variable, so that the afore mentioned single phase may be considered as an insertion compound. The Li⁺ insertion is accompanied by the simultaneous reduction of a part of the Th⁴⁺ ions, resulting in a mixed-valence III/IV thorium fluoride. The electrochemical insertion of Li⁺ ions into the open channels of the host matrix has been carried out at 60 °C, using an alkylcarbonate PC-LiClO₄ 1 M electrolyte. The Li⁺ and Th³⁺ contents, both in the starting composition and the Li⁺ inserted ones, were investigated by high resolution solid state ⁷Li NMR and EPR, respectively.     

Experimental and theoretical study on 3,5‐(oxo/thioxo) derivatives of 2,7‐dimethyl‐1,2,4‐triazepines–iodine molecular complexes

Intermolecular charge‐transfer (CT) spectra of 3‐thioxo‐5‐oxo‐, 5‐thioxo‐3‐oxo‐, and 3,5‐dithioxo‐ derivatives of 2,7‐dimethyl‐[1,2,4]‐triazepine 1:1 molecular complexes with molecular iodine were studied in the UV‐visible region. Equilibrium constants and free energy changes of the formed complexes were determined in solution. Ab initio calculations at HF/LANL2DZ* and MP2/LANL2DZ* were carried out to establish the nature of the complexation site, to determine the complex structures, and to examine the basicity of these compounds toward molecular iodine. The 3,5‐dithioxo‐2,7‐dimethyl‐[1,2,4]‐triazepine is the most basic one toward molecular iodine. In all cases, the complexation takes place at the heteroatom attached to position 3 of the triazepine. Hence, although in general, thiocarbonyls are stronger bases than carbonyls in the gas phase, 5‐thioxo‐2,7‐dimethyl‐[1,2,4]‐triazepin‐3‐one behaves as an oxygen base towards I₂. Experimental free energies in solution and gas‐phase computational values are linearly correlated. Copyright © 2009 John Wiley & Sons, Ltd.     

Biotechnology and In Vitro Culture as an Alternative System for Secondary Metabolite Production

Medicinal plants are rich sources of bioactive compounds widely used as medicaments, food additives, perfumes, and agrochemicals. These secondary compounds are produced under stress conditions to carry out physiological tasks in plants. Secondary metabolites have a complex chemical structure with pharmacological properties. The widespread use of these metabolites in a lot of industrial sectors has raised the need to increase the production of secondary metabolites. Biotechnological methods of cell culture allow the conservation of plants, as well as the improvement of metabolite biosynthesis and the possibility to modify the synthesis pathways. The objective of this review is to outline the applications of different in vitro culture systems with previously reported relevant examples for the optimal production of plant-derived secondary metabolites.     

High Brønsted beta nuc values in SNAr displacement. An indicator of the SET pathway?

Nucleophilic substitutions of 4-chloro-7-nitrobenzofurazan (NBD-Cl) and 3-methyl-1-(4-nitrobenzofurazanyl)-imidazolium ions (NBD-Im+) with a series of 4-X-substituted anilines have been kinetically investigated in 70-30 (v/v) and 20-80 (v/v) H2O-Me2SO mixtures. The rate-limiting step in these reactions is nucleophilic addition with formation of Meisenheimer-type sigma-adducts followed by fast expulsion of the leaving group (Cl- or Im). The reactions are characterized by a notable sensitivity to basicity of the aniline nucleophiles, with Hammett rho values of -2.68 and -3.82 in 30% and 80% Me2SO, respectively, for NBD-Cl and even more negative values, -3.43 and -5.27, respectively, for NBD-Im+. This is consistent with significant development of positive charge at the nitrogen atom of the zwitterionic sigma-adduct. Unexpectedly, the Br?nsted-type plots reveal abnormally high beta nuc values, ca. 1.0 and 1.3-1.4, respectively. Satisfactory correlations between the rates of the reactions and the oxidation potentials of the respective anilines support a SET mechanism for this process, i.e. initial (fast) electron-transfer from the aniline donor to the nitrobenzofurazan acceptor moiety and subsequent (slow) coupling of the resulting cation and anion radicals within the solvent cage with formation of the sigma-adduct. An alternative possible explanation of the high beta nuc values being related to the strong--I effect exerted by the negatively charged 4-nitrobenzofurazanyl structure, which would induce a greater positive charge at the developing anilinium nitrogen atom in the sigma-adduct-like transition state as compared with the situation in the reference protonation equilibria of anilines, is considered less probable. It is thus proposed that obtention of abnormal beta nuc values may be an indicator of electron-transfer in nucleophilic aromatic substitution and highlights the transition from the polar (SNAr) to the single electron-transfer (SET) mechanism.     

Etude du Systeme LiPO3-Pr(PO3)3 Donnees sur LiPr(PO3)4

The LiPO₃-Pr(PO₃)₃ system was studied by micro-differential thermal analysis. The only new compound observed in the system was LiPr(PO₃)₄, melting incongruently at 1246 K. An eutectic appears at 926 K. Crystallographic data and powder diagram of the new compound are given. LiPr(PO₃)₄ crystallizes in the C2/c monoclinic system with unit cell: a=16.428(6), b=7.054(3), c=9.747(4) Å, β=126°31′(3), V=910.2 ų, Z=4. The IR and Raman spectra of this compound are given. This revised version was published online in July 2006 with corrections to the Cover Date.     

The new one‐dimensional coordination polymer catena‐poly[[diaquasodium(I)]‐μ‐oxalato‐[diaquairon(III)]‐μ‐oxalato]

The oxalate dianion is one of the most studied ligands and is capable of bridging two or more metal centres and creating inorganic polymers based on the assembly of metal polyhedra with a wide variety of one‐, two‐ or three‐dimensional extended structures. Yellow single crystals of a new mixed‐metal oxalate, namely catena‐poly[[diaquasodium(I)]‐μ‐oxalato‐κ⁴O¹,O²:O^1′,O^2′‐[diaquairon(III)]‐μ‐oxalato‐κ⁴O¹,O²:O^1′,O^2′], [NaFe(C₂O₄)₂(H₂O)₄]_n, have been synthesized and the crystal structure elucidated by X‐ray diffraction analysis. The compound crystallizes in the noncentrosymmetric space group I4₁ (Z = 4). The asymmetric unit contains one Na^I and one Fe^III atom lying on a fourfold symmetry axis, one μ₂‐bridging oxalate ligand and two aqua ligands. Each metal atom is surrounded by two chelating oxalate ligands and two equivalent water molecules. The structure consists of infinite one‐dimensional chains of alternating FeO₄(H₂OW1)₂ and NaO₄(H₂OW2)₂ octahedra, bridged by oxalate ligands, parallel to the [100] and [010] directions, respectively. Because of the cis configuration and the μ₂‐coordination mode of the oxalate ligands, the chains run in a zigzag manner. This arrangement facilitates the formation of hydrogen bonds between neighbouring chains involving the H₂O and oxalate ligands, leading to a two‐dimensional framework. The structure of this new one‐dimensional coordination polymer is shown to be unique among the A^IM^III(C₂O₄)₂(H₂O)_n series. In addition, the absorption bands in the IR and UV–Visible regions and their assignments are in good agreement with the local symmetry of the oxalate ligand and the irregular environment of iron(III). The final product of the thermal decomposition of this precursor is the well‐known ternary oxide NaFeO₂.     

Synthesis and photovoltaic properties of 2,6‐bis(2‐thienyl) benzobisazole and 4,8‐bis(thienyl)‐benzo[1,2‐B:4,5‐B′]dithiophene copolymers

In an effort to design efficient low‐cost polymers for use in organic photovoltaic cells the easily prepared donor–acceptor–donor triad of a either cis‐benzobisoxazole, trans‐benzobisoxazole or trans‐benzobisthiazole flanked by two thiophene rings was combined with the electron‐rich 4,8‐bis(5‐(2‐ethylhexyl)‐thien‐2‐yl)‐benzo[1,2‐b:4,5‐b′]dithiophene. The electrochemical, optical, morphological, charge transport, and photovoltaic properties of the resulting terpolymers were investigated. Although the polymers differed in the arrangement and/or nature of the chalcogens, they all had similar highest occupied molecular orbital energy levels (?5.2 to ?5.3 eV) and optical band gaps (2.1–2.2 eV). However, the lowest unoccupied molecular orbital energy levels ranged from ?3.1 to ?3.5 eV. When the polymers were used as electron donors in bulk heterojunction photovoltaic devices with PC₇₁BM ([6,6]‐phenyl C₇₁‐butyric acid methyl ester) as the acceptor, the trans‐benzobisoxazole polymer had the best performance with a power conversion efficiency of 2.8%. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 316–324     

Remediation of copper ions from aqueous solution using hybrid magadiite: kinetics,isotherm and mechanism of removal

Research on Chemical Intermediates - This paper deals with the potential use of hybrid magadiite composite as an alternative adsorbent for the removal of copper ions. Na-magadiite was synthesized...     

Study by Differential Scanning Calorimetry of Water-in-Oil Emulsions Stabilized by Clays and CTAB

In this work, we have tested various formulations in order to get emulsions containing pure water, Tunisian olive oil, Tunisian clays, and an ammonium salt. Two different types of clays: smectite and kaolinite and the cethyltrimethylamonium bromide (CTAB) were tested. CTAB is used as surfactant and a compound modifying the clays properties. The amount of CTAB being fixed at 0.66 w/w, the proportions of clays were varied from 0 to 9% for each of the following proportions of water: 10, 20, 30%. To the aqueous phase obtained by mixing two separate aqueous phases: water + CTAB and water + clay, the oil was added drop by drop, the agitation being maintained at 5000 rpm. The obtained mixtures were analyzed by Differential Scanning Calorimetry (DSC), optical microscopy and bottle tests. An optimized formulation containing water (30%), smectite clay (5.3%) and CTAB (0.66%) was found to give W/O emulsions which kinetic stability is greater than 75 days regarding coalescence and greater than 700 hours regarding sedimentation.