- Two novel organic-inorganic hybrid compounds with straight and zigzag chain alignments of Cu(II) centers: Synthesis, crystal structure, spectroscopy, thermal analysis and magnetism
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Abstract Two hybrid salts, viz. bis(guanidinium) bis(oxalato)cuprate(II) (1) and bis(2-aminopyridinium) bis(oxalato)cuprate(II) trihydrate (2) have been synthesized and characterized by elemental and thermal analyses, IR spectroscopy, single-crystal X-ray diffraction and SQUID magnetometry. Compounds 1 and 2 crystallize in the monoclinic P21/c and triclinic P1ˉ space groups, respectively. In both structures, the four-coordinated Cu(II) ion in [Cu(C2O4)2]2- unit weakly interacts with two axial O-atoms of neighboring units to build a prolate CuO6 octahedron, with regular axial Cu-O bonds of 2.825 ? in 1, whereas in 2 two different Cu-O bonds (2.814 ? and 2.701 ?) are found. In 1, stacking of [Cu(C2O4)2]2- units across internal symmetry-related O-atoms results in equidistantly spaced monomers, thus forming straight Cu(II) chains with regular spacing of Cu?Cu = 3.582 ?. By contrast, in 2, stacking of the [Cu(C2O4)2]2- entities occurs via external symmetry-related O-atoms, yielding zigzag Cu(II) chains with shorter intra-dimer spacing of [Cu?Cu]intra = 3.430 ? and longer inter-dimer spacing of [Cu?Cu]inter = 4.961 ?. The anhydrated compound 1 is stable up to 250 °C, whereas the hydrated compound 2 shows a significant weight loss of solvent water molecules at about 70°C, followed by the decomposition of the network. The magnetic measurements in the 2-300 K temperature range revealed weak antiferromagnetic coupling in the two hybrid salts.
- Nenwa, Justin,Djomo, Edith D.,Nfor, Emmanuel N.,Djonwouo, Patrick L.,Mbarki, Mohammed,Fokwa, Boniface P.T.
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- PROCESS FOR PRODUCING METHIONINE
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A process for producing methionine by hydrolysis of 5-(β-methylmercaptoethyl)hydantoin in the presence of an alkali, in which the concentration of hydrogen sulfide is 5 ppm or less in a solution used for hydrolysis comprising 5-(β-methylmercaptoethyl)hydantoin and the alkali, whereby methionine can be stably produced for a long period of time.
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Page/Page column 2
(2008/12/07)
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- Oxidation of Thiourea by Iodate: a New Type of Oligo-oscillatory Reaction
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In the oxidation of thiourea by iodate in weakly acidic solution the concentration of iodide may exhibit several extrema.The number of extrema mainly depends on the initial ratio of the concentrations of thiourea and iodate, and is at most four. the first step of the reaction results in the formation of iodide which then reacts with iodate to give iodine.The latter oxidizes thiourea in several steps, the end products being sulphate ions, ammonium ions, and carbon dioxide.Taking into account the independently determined rate constants for the sub-systems, the change in the concentrations of iodide and iodine with time can be calculated.There is good agreement between the experimental and theoretical curves.
- Rabai, Gyula,Beck, Mihaly T.
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p. 1669 - 1672
(2007/10/02)
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