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51.
Mehrzia Krimi Ammar Tahar Jouini Ahmed Driss 《Journal of chemical crystallography》2000,30(4):265-268
The synthesis and crystal structure of a new three dimensional cobalt(II) complex [Co(C6H12N4)2(H2O)4Co(H2O)6][SO4]2.6H2O are reported. It crystallizes in the triclinic space group P-1 with a = 13.394(3), b = 16.077(3), c = 9.282(2) Å, = 89.71(2), = 90.42(2), = 114.02(2)°, V = 1825.6(7)Å3 and Z = 2. The structure is comprised of [Co(C6H12N4)2 (H2O)4Co(H2O)6][SO4]2 units and H2O molecules. Two molecules of ligand and four molecules of water chelate one type of CoII in an octahedral fashion through two N and four O atoms: the four O atoms form the equatorial plane and the two N atoms occupy the apical positions. The other type of CoII cation is chelated by six water molecules. 相似文献
52.
Rare-earth sesquifluorides with no absorption in visible spectral region, such as LaF3, GdF3, LuF3, YF3, ScF3, are the topic of intense study as a host for luminescence materials. However, except Nd:LaF3, they are not studied as a host for laser materials. The main obstacle troubling further study of GdF3, LuF3, YF3, ScF3 single crystal is the fact that there is first-order phase transition (LaF3 type↔beta-YF3 type for GdF3, alpha-YF3 type↔beta-YF3 type for the rest) between the room and melting temperature.To prevent the phase transition, first of all, we have tried to make solid solution between GdF3 and YF3 in such a way that the average cation radii can be shifted to the size that does not have phase transition. Ce3+ perturbed luminescence was observed in the Ce- and Sr-codoped GdF3-YF3 system. Similar solid solution concept was applied to the combination between GdF3 and YbF3. The emission spectrum of Yb3+ that exhibits broad bands around 1 μm was observed. Room temperature up-conversion luminescence spectra of Pr3+-doped Gd1−xYbxF3 were studied and visible emission from Pr3+ was obtained under infrared laser pumping in the Yb3+ broad absorption band at 935.5 nm. 相似文献
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The synthesis method, crystal structure determination, phase transitions studied by thermal analysis and IR spectrometric investigation of 2C6H9N2+.SO42– are reported. The compound crystallizes in the monoclinic space group C2/c (no. 15) with a = 10.5068(4) Å, b = 10.2225(5) Å, c = 14.0422(7) Å, and β = 104.489(3)°. The atomic arrangement can be described by layers built by all the components of the structure and centered by planes z = 1/4 and 3/4. The organic molecules form channels parallel to the c direction with dimensions of 4.163(1)Å and 5.148(4)Å. Thermal analysis shows that the anhydrous compound presents an irreversible weak phase transition. The IR study, based on theoretical analyses and on the literature data allows the interpretation of the IR spectrum. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
55.
Chafia Sobhi Abdelmalek Khorief Nacereddine Abdelhafid Djerourou M. José Aurell Luis R. Domingo 《Tetrahedron》2012,68(40):8457-8462
The role of the trifluoromethyl group in reactivity, regio-, and stereoselectivity in cycloaddition reactions has been analyzed by studying the 1,3-dipolar cycloaddition (13DC) reactions of nitrone 4 with 3,3,3-trifluoro-1-nitropropene 7b and 3,3,3-trifluoro-2-nitropropene 14 using density functional theory (DFT) methods at the B3LYP/6-311G(d) level. The recent M06-2X functional has also been evaluated but, although the thermodynamic performance is improved, the kinetic data are not necessarily better than those obtained by the popular B3LYP functional for cycloaddition reactions. Four reactive channels associated with the meta and ortho regio- and endo and exo stereoselective approach modes of the nitro group of these disubstituted ethylenes relative to nitrone 4 have been explored and characterized. Unlike other electron-withdrawing groups, the trifluoromethyl group increases the reactivity of the nitroethylene, but it does not modify the meta and endo selectivities when it is located at the β conjugated position of nitroethylene. Analysis of the global and local electrophilicity indices allows for an explanation of the role of the trifluoromethyl group in reactivity and regioselectivity of electrophilically activated ethylenes. 相似文献
56.
Mathieu Lazerges Kathleen Isabelle Chane-Ching Salah Aeiyach Saloua Chelli Brigitte Pepin-Donat Martial Billon Christian Lombard François Maurel Mohamed Jouini 《Journal of Solid State Electrochemistry》2009,13(2):231-238
The electrochemical oxidation of hexa-N-pyrrolylbenzene in organic media leads, via intramolecular coupling of the pyrrole residues, to the deposition of a molecular
semiconductor film on an electrode surface. In situ electron spin resonance–electrochemical experiments reveal that the semiconductor
is endowed with both properties of conducting polymers (i.e., reversible oxidation) and polyaromatic molecular materials (i.e., highly paramagnetic). The material, which is easy to process as soft homogeneous thin film, shows a tunable 0 to 1 spin
concentration per molecule at room temperature by controlling the electrochemical potential.
Contribution to the Fall Meeting of the European Materials Research Society, Symposium D: 9th International Symposium on the
Electrochemical–Chemical Reactivity of Metastable Materials, Warsaw, 17th–21st September, 2007.
An erratum to this article can be found at 相似文献
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Mechouet M Perruchot C Maurel F Aeiyach S Bucher C Chardon S Jouini M 《The journal of physical chemistry. A》2012,116(3):970-978
The electrochemical and spectroelectrochemical properties of N,N-diphenyl-1,4-phenylenediamine (PDA) were investigated in the absence and in the presence of 18-crown-6-ether (18C6) or dibenzo 24-crown-8-ether (DB24C8), in a solution of tetrabutylammonium hexafluorophosphate (TBAPF6) in acetonitrile and in the presence of trifluoroacetic acid (TFA) only for 18C6. In neutral acetonitrile, PDA undergoes two reversible oxidation processes, which lead first to the formation of the cation-radical considered as mixed valence (MV) compound, and then to the dicationic species. When 18C6 is added in the medium and depending on 18C6 concentration, cyclic voltammetry shows a marked shift to more cathodic potentials of the current waves of the second redox process only. This is attributed to a strong interaction between the PDA(+2) dication and two 18C6 molecules, leading to the formation of a supramolecular complex with an association constant value K(a) = 7.0 × 10(7) M(-2). The interaction of 18C6 with PDA(+2) dication has a direct effect on the PDA(+.) cation-radical corresponding to a decrease in the lifetime of the MV compound and of the intramolecular electron transfer rate when 18C6 is present. Indeed, it results in a large decrease in the intervalence charge transfer (IV-CT) between the two amine centers in the MV compound (k(th) = 1.35 × 10(10) s(-1) in 18C6-free neutral solution containing 5.0 × 10(-4) M PDA, and k(th) = 3.6 × 10(9) s(-1) in the same medium at [18C6]/[PDA] = 20/1). And the comproportionation constant K(co) falls from 6.0 × 10(6) in 18C6-free solution to 1.6 × 10(3) at [18C6]/[PDA] = 20/1. In acidified acetonitrile and when TFA concentration is increased, PDA still shows the two successive and reversible oxidation processes, but both are shifted to more anodic potentials. However, when 18C6 is added, the two oxidation waves shift to more cathodic potentials, indicating an interaction of all protonated PDA redox states with 18C6, resulting in the formation of supramolecular complexes. In the presence of TFA, the value of K(co) is decreased to 4.3 × 10(4), but it remains unchanged when 18C6 is added, indicating no change in the lifetime of the MV compound. In this medium, IV-CT in the MV compound is greater with 18C6 (k(th) = 2.3 × 10(10) s(-1) for [18C6]/[PDA] = 20/1) than without (k(th) = 1.4 × 10(9) s(-1)), which indicates a more important IV-CT rate when 18C6 is present. The results show for the first time that is it possible to control the IV-CT rate, through the lifetime and the potential range where the MV compound is the most important. This control is not obtained as usual by chemical modification of the structure of the starting molecule, but by varying either the acidity or the 18C6 concentration as external stimuli, which lead to reversible formation/dissociation of a supramolecular complex species. Moreover, we also studied the electrochemical properties of PDA in the presence of wider crown ether such as DB24C8. We showed that PDA undergoes the same electrochemical behavior with DB24C8 than with 18C6 in neutral organic medium (K(a) = 2.9 × 10(3) M(-1)). This result suggests that the complexation between the electrogenerated PDA(+2) dication and the crown ethers may occur through face-to-face mode rather than rotaxane mode even with DB24C8 which is supposed to form inclusion complexes. 相似文献