Department of Chemistry

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IIT Hyderabad

Li0.53Na0.03MnO2 compound was prepared by ion exchange from Na0.7MnO2 which was synthesized by the sol-gel method using glycolic acid as a chelating agent. Powder X-ray diffraction and transmission electron microscopy (TEM) confirmed the structure of the as-prepared material resembled that of spinel with a high degree of disorder in the (111) planes. The material delivered a discharge capacity of 200 mA h g-1 after 50 cycles and showed excellent cyclability without undergoing the typical capacity fading exhibited by normal spinel material. It is speculated that the stacking disorder and small particle size of the prepared Li0.53Na0.03MnO2 powder have contributed to prevent the symmetry-breaking transformation which is believed to be responsible for capacity fading.

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Journal of Materials Chemistry

Structural and electrochemical characteristics of nano-structured Li0.53Na0.03MnO2 manganese oxide prepared by the sol-gel method

The ion exchange route was first successfully used by Livage et al. for depositing WO3 films exhibiting reversible electrochromic effect. We report in this paper the preparation of a solid precursor material by chemically modifying this route. The short lived ion exchange derived sol on addition of H2O2 and acetic acid on further processing, yields a solid precursor material with (1) unusually enhanced stability and (2) easy solvation in alcohol. UV and infrared spectroscopic investigations give strong evidence for these two properties as manifestations of the lower degree of polymerization and coordination of the acetate ion as a chelating ligand with the tungsten atom.

Journal of Sol-Gel Science and Technology

Ion exchange derived precursor materials for deposition of WO3 electrochromic films: Spectroscopic investigations

Liquid electrolytes comprising lithium salts of the type LiX (X=N(CF3SO2)2, ClO4) dissolved in an aprotic solvent PC and a binary mixture of PC and EC show σ25(max) of the order of 10-2 S cm-1. Gel electrolytes synthesized by the incorporation of PMMA up to 25 wt.% in these liquid electrolytes show insignificant changes in the σ25 value, retaining the liquid-like behaviour with σ25(max) ∼ 10-3 S cm-1. The small σ25 decline in contrast to the dramatic η25 increase upon PMMA incorporation in liquid electrolytes exemplifies that PMMA plays a nonsolvating, passive role in these systems. The conduction mechanism that persists in liquid electrolytes is apparently preserved in gel electrolytes based on PMMA. Gel electrolytes can be visualized as highly viscous liquid electrolytes encaged in a polymeric matrix as thermal dependence of conductivity and viscosity for liquid and gel electrolytes follow nearly the same trend. PMMA imparts mechanical stability to gels thereby promoting ease of device fabrication. Nominal variance of conductivity over a wide temperature range makes these gel electrolytes ideal candidates for electrochromic windows (ECWs). © 2002 Elsevier Science B.V. All rights reserved.

Solid State Ionics

Conductivity and viscosity of liquid and gel electrolytes based on LiClO4, LiN(CF3SO2)2 and PMMA

Nonaqueous unimolar solutions of lithium perchlorate (LiClO4) and lithium trifluoromethanesulfonate or triflate (LiCF3SO3) in γ-butyrolactone (γBL) mixed in (a) 1:1 and (b) 3:2 volume ratios yield mixed salt electrolytes with good conductivity performance with σ25 approaching 10-2 S cm-1. Addition of 10 wt.% of poly(methylmethacrylate) (PMMA) to these liquid electrolytes manifests in producing highly viscous gel electrolytes with η25 in the range of 104-105 cSt and σ25 greater than 10-3 S cm-1. Conductivity and viscosity studies reveal that PMMA plays an insignificant role in controlling the conduction mechanism in gel electrolytes, as they tend to retain the liquid-like behaviour. Also, the dimensional strength bestowed to gels by the polymer stimulates their use in electrochromic windows (ECWs). Inconsequential variation of σ over the operational temperature range of an ECW renders them to be ideal candidates for the same. © 2002 Elsevier Science B.V. All rights reserved.

Effect of mixed salts on the properties of gel polymeric electrolytes

FTIR spectroscopy and ionic conductivity measurements have been employed to study the solvation and conduction mechanism of lithium ions in aprotic liquid electrolytes of LiCF3SO3-PC (lithium trifluromethanesulfonate-propylene carbonate) and gel electrolytes containing poly(methylmethacrylate) (PMMA) additionally. Cation solvation occurs via interactions between Li+ ions with the ring oxygens as well as the carbonyl oxygen of PC molecules over the entire salt concentration range under investigation (0.025-2 M) for both liquid and gel electrolytes. The ionic conductivity decline for concentrations ≥0.8 M LiCF3SO3-PC is attributed to the formation of ion pairs and/or triplets. Presence of (a) free CF3SO3- ions in 0.025 and 0.05 molar LiCF3SO3-PC solutions, (b) the LiCF3SO3 structure with a monodentate coordinated lithium ion for concentrations ≥0.5 molar LiCF3SO3-PC systems and (c) ion triplets comprising two cations and an anion with a bidentate bridging structure in 2 M LiCF3SO3-PC electrolytes, has been established. Ionic conductivity performance concurs with our infrared results. Gel electrolytes containing upto 15 wt% of PMMA have been found to exhibit liquid like behavior but 2 M LiCF3SO3-PC systems that incorporate 25 wt% of polymer show a distinct Li+-O=C (of PMMA) interaction which is unambiguously determined from the remarkable changes observed for the νs(C=O) and νs(SO3) - the symmetric stretching vibrational modes. © 2002 Kluwer Academic Publishers.

Journal of Materials Science

FTIR investigations on ion-ion interactions in liquid and gel polymeric electrolytes: LiCF3SO3-PC-PMMA

The tricyclic α-keto hemiacetals 3a,b and 8a-d obtained from ruthenium-catalyzed oxidation of tetrahalonorbornyl derivatives possessing a pendant hydroxymethyl group were cleaved using Pb(OAc)4 or alkaline H2O2 to give γ-lactone-fused cyclopentane derivatives 5a,b and 9a-d. The α-keto hemiacetal 3b has also been elaborated to spiroepoxide derivative 25. The stable hydrate 4 formed from ruthenium-catalyzed oxidation of acrolein adduct 10 furnished an intramolecular hemiacetal 11 upon cleavage with Pb(OAc)4. The α-halo ester moiety in 5a was transformed smoothly in a highly regio- and stereoselective manner to α-hydroxy esters through a lactone-assisted intermediate to furnish 18.

Journal of Organic Chemistry

An easy access to γ-lactone-fused cyclopentanoids

A highly oxygenated, novel pentacyclic bis-oxa-bridged compound 8 was synthesized with remarkable efficiency starting from readily available tetrachloro-5,5-dimethoxyclopentadiene and 1,4-cyclohexadiene in three steps. The ruthenium-catalyzed oxidation of 2:1 bis-adduct 1 followed by a one-pot transformation of the resulting bis-α-diketone 3 furnished (after esterification) the title compound in an overall yield of 29.1%. The versatility of this simple method was further demonstrated with other norbornyl α-diketones to obtain the corresponding strained oxa-bridged derivatives. Copyright © 2002 American Chemical Society.

Journal of the American Chemical Society

Synthesis of a novel, highly symmetric bis-oxa-bridged compound

Innovative structured catalytic packings have been prepared by in situ hydrothermal synthesis of mesoporous MCM-41 on stainless steel grid. After a one-step synthesis, the metal support was observed to be homogeneously covered by a dense layer (∼80μm) of the mesoporous material. 2002 Published by Elsevier Science B.V.

Catalysis Communications

Synthesis and characterization of MCM-41 coatings on stainless steel grids

The tetranucleating manganese(III) and copper(II) complexes of the type Mn4LP2, Cu4LP2, where H6LP2 = 1,4 bis[2′- hydroxy-3′-(iminotetraphenylporphyrin)-5′-methylbenzyl] piperazine, were synthesized and characterized. Mn4LP2 complex is EPR silent and this indicates that manganese is in +3 oxidation state. Cu4LP2 complex showS broad band with g value centered at 2.06 indicates antiferromagnetic coupling. Cyclic voltammetry studies indicating that the Mn4LP2 complex undergoes quasireversible electron transfer in the cathodic potential region and irreversible electron transfer in the anodic potential region. Cu4LP2 complex undergoes irreversible electron transfer in the cathodic potential region, quasireversible electron transfer in the anodic potential region.

Indian Journal of Chemical Technology

Synthesis, spectral and electrochemical studies of novel porphyrin bound tetranuclear acyclic manganese(III) and copper(II) complexes

Alcoholic solutions of acetylated peroxotungstic acid (APTA) and oxylated APTA (ox-APTA) precursors are used for casting films by a spin coating technique. Fourier transform infrared (diffuse reflectance mode) spectroscopy is used to investigate the linkages prevalent in the constituents of the films in the as-deposited as well as annealed states. The modes of association of peroxo and acetate/oxalate in the form of bidentate, chelating or bridging ligands is highlighted. The spectra clearly reveal the gradual decomposition of peroxo and organic ligands and also the hydrated state of film at various stages of the annealing treatment. Films based on ox-APTA precursor exhibit better electrochromic performance in contrast to films based on APTA alone. This feature of ox-APTA films which is of enormous practical importance, has been established by spectral studies, as heat-treated ox-APTA films have a microstructure which is entirely different from that of heat-treated APTA films. © 2001 Elsevier Science B.V. All rights reserved.