• Volume 123, Issue 1

January 2011,   pages  5-89

• Synthesis, structure and ionic conductivity in scheelite type Li0.5Ce$_{0.5−x}$Ln$_x$MoO4 ($x = 0$ and 0.25, Ln = Pr, Sm)

Scheelite type solid electrolytes, Li0.5Ce$_{0.5−x}$Ln$_x$MoO4 ($x = 0$ and 0.25, Ln = Pr, Sm) have been synthesized using a solid state method. Their structure and ionic conductivity (𝜎) were obtained by single crystal X-ray diffraction and ac-impedance spectroscopy, respectively. X-ray diffraction studies reveal a space group of $I4_1/a$ for Li0.5Ce$_{0.5−x}$Ln$_x$MoO4 ($x = 0$ and 0.25, Ln = Pr, Sm) scheelite compounds. The unsubstituted Li0.5Ce0.5MoO4 showed lithium ion conductivity $\sim 10^{−5}-10^{−3} \Omega^{−1}$cm-1 in the temperature range of 300-700°C ($\sigma = 2.5 \times 10^{−3} \Omega^{−1}$cm-1 at 700°C). The substituted compounds show lower conductivity compared to the unsubstituted compound, with the magnitude of ionic conductivity being two (in the high temperature regime) to one order (in the low temperature regime) lower than the unsubstituted compound. Since these scheelite type structures show significant conductivity, the series of compounds could serve in high temperature lithium battery operations.

• Laser flash photolysis study on 9-phenylxanthenium tetrafluoroborate: Identification of new features due to the triplet state

Laser flash photolysis study on highly fluorescent and stable salt of 9-phenylxanthenium cation in neutral condition has been carried out for the first time. A new transient absorption band of this extensively studied system that perhaps remained buried under the fluorescence envelope and hitherto undetected has been identified and attributed to the triplet state of the system. This oxygen-insensitive triplet-triplet absorption band in the 480-600 nm range is expected to trigger new studies exploring the reactivity of the triplet state of this system, which has so far received very little attention.

• A quasiclassical trajectory analysis of stereodynamics of the H+FCl ($v=0- 3$, $j=0- 3$) → HCl+F reaction

The chemical stereodynamics for the title reaction are studied by the quasiclassical trajectory method. Employing the recent works of Deskevich, Hayes, Takahashi, Skodje, and Nesbitt (DHTSN) potential energy surface of the ground $1^2$A' electronic state, the present work calculates the polarizationdependent differential cross sections and the three angular distributions which describe the vector correlations among the product angular momentum j' and the reagent and the product initial relative velocities k and k'. The effect of vibrational and rotational excitations for the reagent FCl and the influence of collision energies on the stereodynamical quantities are also investigated and discussed.

• Metathesis of carbon dioxide and phenyl isocyanate catalysed by group(IV) metal alkoxides: An experimental and computational study

The insertion reactions of zirconium(IV) 𝑛-butoxide and titanium(IV) 𝑛-butoxide with a heterocumulene like carbodiimide, carbon dioxide or phenyl isocyanate are compared. Both give an intermediate which carries out metathesis at elevated temperatures by inserting a second heterocumulene in a head-to-head fashion. The intermediate metallacycle extrudes a new heterocumulene, different from the two that have inserted leading to metathesis. As the reaction is reversible, catalytic metathesis is feasible. In stoichiometric reactions heterocumulene insertion, metathesis and metathesis cum insertion products are observed. However, catalytic amounts of the metal alkoxide primarily led to metathesis products. It is shown that zirconium alkoxides promote catalytic metathesis (isocyanates, carbon dioxide) more efficiently than the corresponding titanium alkoxide. The difference in the metathetic activity of these alkoxides has been explained by a computational study using model complexes Ti(OMe)4 (1bTi) and Zr(OMe)4 (1bZr). The computation was carried out at the B3LYP/LANL2DZ level of theory.

• High spectral response heteroleptic ruthenium (II) complexes as sensitizers for dye sensitized solar cells

Heteroleptic ruthenium(II) bipyridyl complex, cis-Ru(II)(4,4'-bis(4-tert-butylstyryl)-2,2'-bipyridyl) (4,4'-dicarboxy-2,2'-bipyridyl) (NCS2) (H112) was synthesized and characterized by 1H-NMR, MASS, Spectrofluorometer and UV-Vis spectroscopes. The photo-voltaic performance of the sensitizer was evaluated in Dye Sensitized Solar Cell (DSSC) under irradiation of AM 1.5 G solar light and the photovoltaic characteristics were compared with those of reference cells of HRS1 and N719 fabricated under comparable conditions. Compared to N719, H112 sensitizer showed enhanced molar extinction coefficient and relatively better monochromatic incident photon-to-current conversion efficiency (IPCE) across the spectral range of 400 to 800 nm with solar energy-to-electrical conversion efficiency (𝜂) of 2.43% [open circuit photovoltage (VOC) = 0.631V, short-circuit photocurrent density (JSC) = 8.96 mA/cm2, fill factor (ff) = 0.430], while 𝜂 values of 2.51% (VOC = 0.651V, JSC = 9.41 mA/cm2, ff = 0.410) and 2.74% (VOC = 0.705 V, JSC = 8.62 mA/cm2, ff = 0.455) were obtained for HRS1 and N719 sensitized solar cells respectively. The introduction of 4,$4'$-bis(4-tert-butylstyryl) moieties on one of the bipyridine moieties of N719 complex shows higher light absorption abilities, IPCE and JSC.

• Ce0.98Pd0.02O$_{2-\delta}$: Recyclable, ligand free palladium(II) catalyst for Heck reaction

Palladium substituted in cerium dioxide in the form of a solid solution, Ce0.98 Pd0.02 O1.98 is a new heterogeneous catalyst which exhibits high activity and 100% trans-selectivity for the Heck reactions of aryl bromides including heteroaryls with olefins. The catalytic reactions work without any ligand. Nanocrystalline Ce0.98 Pd0.02 O1.98 is prepared by solution combustion method and Pd is in +2 state. The catalyst can be separated, recovered and reused without significant loss in activity.

• Synthesis, properties and supramolecular structure of piperazinediium thiosulfate monohydrate

Aqueous reaction of ammonium thiosulfate with piperazine (pip) results in the formation of the title compound (pipH2)[S2O3]$\cdot$H2O 1 (pipH2 = piperazinediium) in good yield. 1 was characterized by elemental analysis, IR, Raman andNMRspectra, X-ray powder pattern and its structure was determined. On heating at 100°C, 1 transforms to anhydrous piperazinediium thiosulfate 2, which can be rehydrated to the monohydrate on exposure tomoisture. The structure of 1 consists of two crystallographically independent piperazinediium (pipH2)2+ cations located on inversion centers, a thiosulfate anion and a lattice water. The organic cations, thiosulfate anion and lattice water are linked by six varieties of hydrogen bond namely O-H$\cdots$O, O-H$\cdots$S, N-H$\cdots$O, N-H$\cdots$S, C-H$\cdots$O and C-H$\cdots$S, leading to the formation of alternating layers of (pipH2)2+ cations and water linked thiosulfate chains. A comparative study of several compounds charge balanced by the piperazinediium cation is described.

• Nitration of phenolic compounds and oxidation of hydroquinones using tetrabutylammonium chromate and dichromate under aprotic conditions

In this work, we have reported a mild, efficient and selective method for the mononitration of phenolic compounds using sodium nitrite in the presence of tetrabutylammonium dichromate (TBAD) and oxidation of hydroquinones to quinones with TBAD in CH2Cl2. Using this method, high yields of nitrophenols and quinones were obtained under neutral aprotic conditions. Tetrabutylammonium chromate (TBAC) can also be used as oxidant at same conditions.

• A facile microwave-assisted synthesis of 8,9-cycloalkathieno[3,2-$e$] [1,2,4]triazolo[1,5-𝑐]pyrimidin-5(6𝐻)-ones

A new series of fused thieno[3,2-$e$][1,2,4]triazolo[1,5-𝑐]pyrimidinones was synthesized by condensation of ethyl-3-cyano-4,5,6,7-tetrahydrobenzo[𝑏]thiophene-2-yl carbamate with aryl acid hydrazides in quantitative yields using a facile, one-pot procedure under microwave-assisted conditions.

• A versatile and an efficient synthesis of 5-substituted-1𝐻-tetrazoles

A simple, efficient and a versatile method for the synthesis of 5-substituted-1𝐻-tetrazoles by a [3+2]-cycloaddition reaction of arylnitriles with sodium azide in DMF using ZrOCl2·8 H2O as catalyst has been developed. The reactions work well at 100°C and give the desired products in excellent yield. The examples studied include arylnitriles having electron donating as well as electron releasing groups on the arene nucleus.

• Pendant triazole ring assisted mesogen containing side chain liquid crystalline polymethacrylates: Synthesis and characterization

Two series of click chemistry assisted alkoxymethyl-1H-[1,2,3]-triazol-1-yl containing sidechain liquid-crystalline polymethacrylates were synthesized by free radical polymerization technique. Mesogen was linked to backbone through various spacer units. Monomers and polymers were characterized by FT-IR, 1H and 13C-NMR spectral techniques. Thermal stability of polymers was confirmed by thermogravimetric analysis. Mesomorphic property and phase transition temperature of polymers were analysed by differential scanning calorimetry and polarized optical microscopy. Phase transition temperature and mesomorphic property of polymers with respect to insertion of polar alkoxy group on terminal triazole ring and spacer length between backbone and mesogen were investigated. Polymers exhibited grainy like textures under polarized optical microscopy. Spacer length between mesogen and backbone alters phase transition temperature of the polymers.

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Posted on July 25, 2019