Search results for "Monoclinic crystal system"
showing 10 items of 344 documents
Microheterogeneous electrocatalytic chiral recognition at monoclinic vanadium-doped zirconias: enantioselective detection of glucose.
2007
Synthetic tetragonal and monoclinic vanadium-doped zirconias (t- and m-VxZr1-xO2, 0.005x0.150) exert an effective catalytic effect toward the electrochemical oxidation of glucose in aqueous alkaline media. The catalytic effect of monoclinic specimens attached to carbon and fluorine-doped tin oxide electrodes exhibits a remarkable enantioselectivity, so that catalytic currents for the oxidation of L-glucose at +0.92 V vs AgCl/Ag are considerably larger than those obtained for the oxidation of D-glucose. This enantioselectivity can be associated with the existence of a noncentrosymmetric coordination of vanadium centers in the monoclinic crystalline form of zirconia. From the electrochemical …
Synthesis, characterization and thermal behavior of nine new -type quaternary ammonium tetrafluoroborate or hexafluorophosphate salts prepared by met…
2008
Abstract Nine new quaternary ammonium tetrafluoroborate or hexafluoroborate salts were prepared from analogous bromide or chloride salts using anion exchange reaction in which the corresponding bromide or chloride salt was treated with HBF4 or HPF6 acid in aqueous solutions. The characterizations were performed by 1H NMR and 13C NMR spectroscopy as well as by elemental analysis. The single crystals of three tetrafluoroborate and two hexafluorophosphate salts were obtained by slow evaporation from a methanol/ethyl acetate solution and the crystal structures were determined by X-ray single crystal diffraction. Four of the compounds crystallized in the orthorhombic and one in the monoclinic cr…
A cyano-bridged bimetallic ferrimagnet: Synthesis, X-ray structure and magnetic study
2010
Mixing of trans-[Mn(cyclam)Cl2]Cl (cyclam = 1,4,8,11-tetraazacyclotetradecane) and potassium hexacyanochromate (K3[Cr(CN)6]) aqueous solutions instantaneously yields a 1D infinite chain complex {[Mn(cyclam)(l-CN)2Cr(CN)4]� H2O}n (1). The crystal structure of 1, crystallizing in the monoclinic system with space group P21/n has been solved from X-ray powder diffraction data following direct space approach and refined by the Rietveld method. The structure analysis of 1 reveals alternating [Cr(CN)6] 3� and [Mn(cyclam)] 3+
Synthesis and structural and ionic conductivity studies of Na2ZrSi4O11
1996
The compound Na 2 ZrSi 4 O 1 1 has been prepared both by solid state synthesis and by the sol-gel technique via alkoxides. The structure of Na 2 ZrSi 4 O 11 was investigated by the Rietveld method using X-ray diffractometer data. The powder diffraction data show evidence for a triclinic distortion of the basic monoclinic structure. The ionic conductivity has been determined in the temperature interval 130-560°C using a.c. impedance measurements. The Na + ion mobility is limited, with E a =1.04 eV and σ(300°C)= 2-9 10 7 S/cm. Samples with Ta partially substituted for Zr, according to the formula Na 2-x (Zr 1-x Ta x )Si 4 O 11 with x ≤0.2, showed the same evidence for a triclinic distortion. …
Orthorhombic polymorphs of twotrans-4-aminoazoxybenzenes
2002
The two isomeric compounds 4-amino-ONN-azoxybenzene [or 1-(4-aminophenyl)-2-phenyldiazene 2-oxide], i.e. the alpha isomer, and 4-amino-NNO-azoxybenzene [or 2-(4-aminophenyl)-1-phenyldiazene 2-oxide], i.e. the beta isomer, both C(12)H(11)N(3)O, crystallized from a polar solvent in orthorhombic space groups, and their crystal and molecular structures have been determined using X-ray diffraction. There are no significant differences in the bond lengths and valence angles in the two isomers, in comparison with their monoclinic polymorphs. However, the conformations of the molecules are different due to rotation along the Ar-N bonds. In the alpha isomer, the benzene rings are twisted by 31.5 (2)…
Cation Environment in BaCeO3-Based Protonic Conductors: a Computational Study
2009
Geometry calculations were performed on pure BaCeO(3) fragments and on Y- and In-doped derivatives. HF and DFT approaches were used to investigate monoclinic and orthorhombic structures. The computational methods, structural models, and electronic structure investigation protocols were tuned taking into consideration and balancing the consistency of the results against the computational cost. The calculated structures and energetics parameter, as well as the detailed orbital analysis performed on the corresponding BaCeO(3) derivatives allowed us to explain experimental findings and to develop a procedure to study the cationic octahedral environment of doped X:BaCeO(3) (X = Y, In) and undope…
Unique Bridging Function of the Triazole Core in Copper(II) Chloride Complexes with 1-Allylbenzotriazole
2005
During alternating-current electrochemical synthesis of copper(I) π-complex of [CuCl{C6H4N3(C3H5)}] composition, starting from ethanol solution, containing CuCl2·2H2O and 1-allylbenzotriazole, green crystals of intermediate [CuII3Cl6{C6H4N3(C3H5)}4] (I) compound has been obtained upon 24 h. After some days these crystals transform into red ones of [CuII2Cl4{C6H4N3(C3H5)}3] (II). Both compounds were X-Ray structurally investigated. Crystals of I are triclinic, sp.gr. a = 9.1329(9), b = 10.0352(4), c = 12.239(3) A, α = 76.443(13), β = 84.470(14), γ = 76.808(7)°, V = 1060.5(3) A3, R = 0.0414 for 3311 reflections. II: monoclinic, C2/c, a = 13.828(1), b = 15.044(2), c = 10.702(1) A, β = 91.36(1)…
Facile synthesis of 5β-cholane-sym-triazine conjugates starting from metformin and bile acid methyl esters: Liquid and solid state NMR characterizati…
2009
Abstract Four bile acid-triazine conjugates: N2′,N2′-dimethyl-6′-(3α-hydroxy-5β-24-norcholyl)-1′,3′,5′-triazine-2′,4′-diamine (lithocholyl triazine, 4a), N2′,N2′-dimethyl-6′-(3α,7α-dihydroxy-5β-24-norcholyl)-1′,3′,5′-triazine-2′,4′-diamine (chenodeoxycholyl triazine, 4b), N2′,N2′-dimethyl-6′6′-(3α,12α-dihydroxy-5β-24-norcholyl)-1′,3′,5′-triazine-2′,4′-diamine (deoxycholyl triazine) (4c), and N2′,N2′-dimethyl-6′-(3α,7α,12α-trihydroxy-5β-24-norcholyl)-1′,3′,5′-triazine-2′,4′-diamine (cholyl triazine) (4d) have been prepared and characterized by liquid and solid state NMR. An improved synthetic method produced better yields and an easier purification procedure for 4d than reported in the liter…
Variable-temperature X-ray crystal structure determinations of {Fe[tren(6-Mepy)3]}(ClO4)2and {Zn[tren(6-Mepy)3]}(ClO4)2compounds: correlation of the …
2007
Variable-temperature X-ray crystal structure determinations (80–330 K) on compounds {Fe[tren(6-Mepy)3]}(ClO4)2(1-Fe) {tren(6-Mepy)3is tris[3-aza-4-(6-methyl-2-pyridyl)but-3-enyl]amine} and {Zn[tren(6-Mepy)3]}(ClO4)2(1-Zn) {tren(6-Mepy)3is tris[3-aza-4-(6-methyl-2-pyridyl)but-3-enyl]amine} were carried out together with a detailed analysis of the unit-cell volume and parameters in the spin transition region for (1-Fe). Both compounds crystallize in the monoclinic system and retained the space groupP21/cat all measured temperatures. The Fe and Zn atoms are surrounded by six N atoms belonging to imine groups and pyridine groups of the trifurcated ligand, adopting a pseudo-octahedral symmetry. …
Synthesis, crystal structure and magnetic properties of the complex [ReCl3(tppz)]·MeCN
2015
The reaction of the starting materials [ReIIICl3(MeCN)(PPh3)2] or [ReVOCl3(PPh3)2] with 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz) in acetonitrile yielded the Re(III) complex [ReCl3(tppz)]·MeCN (1). This complex crystallizes in the monoclinic space group P21/n and its crystal structure consists of neutral mononuclear entities with meridional geometry of the chloride ligands, and the six-coordination of the Re(III) ion being completed by the tridentate tppz ligand. Each metal centre exhibits a highly distorted octahedral coordination with Re–Cl and Re–Ntppz bond lengths covering the ranges 2.3590(9)–2.3606(8) and 1.971(2)–2.096(2) A, respectively. The magnetic properties of 1 have been inves…