M. Padmanabhan

Catalytic properties of cobalt(II) porphyrins supported on styrene-divinylbenzene copolymer

Polymeric pyridinium chloride was synthesized by treating pyridine with 2% divinylbenzene (DVB)-crosslinked chloromethyl polystyrene. Sodium 5,10,15,20-tetrakis(4-sulfophenyl)porphyrin was synthesized and appended on the above polymer through an ionic linkage. Cobalt(II) complex of the polymeric porphyrin was synthesized and characterized chemically and spectroscopically. This complex was employed as catalyst for the oxidation of dithiocarbamates to thiuram disulfide. Electronic and ESR spectra of the complex were analyzed before and after catalysis. pH dependence of catalytic reactions was also studied. These studies provide evidence for the catalytic ability of the polymeric cobalt(II) porphyrin system. A mechanism for the catalytic reaction is suggested on the basis of the above results.

CO catalytic oxidation by a metal organic framework containing high density of reactive copper sites

A new metal organic framework containing high density of active Cu sites demonstrates 100% oxidative conversion of CO to CO(2).

Peroxidase-like catalytic activities of ionic metalloporphyrins supported on functionalised polystyrene surface

Metalloderivatives of anionic tetrasulphonated tetraphenylporphyrin (MTPPS, M = Mn(III), Fe(III) and Co(III)) were synthesized and immobilized on cationically functionalised divinylbenzene(DVB)-crosslinked polystyrene(PS). These supported catalysts (PS-MTPPS) were found to exhibit peroxidase-like activity. The co-oxidation of 4-aminoantipyrine and phenol by H2O2 was attempted with these catalysts to mimic this enzyme function. The catalytic efficiency of all these immobilized MTPPS was found to be superior to the corresponding unsupported MTPPS in solution. The effect of the central metal ion of the porphyrin, pH of the reaction medium and also the temperature effect are investigated. The ideal pH was seen to be in the 8.0–8.5 range, with maximum effect at 8.2. The efficiency order for the various PS-MTPPS was seen to be Co>Mn>Fe, with CoTPPS showing efficiency comparable to that of horseradish peroxidase. The catalytic efficiency was found to be increasing with temperature for all the catalysts. The re-usability of these PS-MTPPS systems for peroxidase-like activity was also studied and it was found that they exhibited a very high degree of recyclability without much poisoning.

New polyoxomolybdate compounds synthesized in situ using ionic liquid 1-butyl-3-methyl-imidazolium tetrafluoroborate as green solvent

Herein we report the facile, green syntheses of three new polyoxomolybdate-based inorganic–organic hybrid materials using room temperature ionic liquid (RTIL), 1-butyl-3-methyl-imidazolium tetrafluoroborate (bmim)[BF4], as a green and reactive solvent. The organic imidazolium component of the RTIL was incorporated into all three structures, the μ5-oxo octamolybdate cluster compound (bmim)3NH4[Mo8O26] (1) and two Keggin-type cluster compounds, one being a charge transfer salt (bmim)4[PMoVMo11O40] (2) and the other having the unreduced anion (bmim)3[PMo12O40] (3). Phase pure and highly crystalline samples were obtained. In 1 the Mo8O26 moiety is a tetranionic cluster in its β phase. Compound 1 contains three bmim cations and an NH4+ molecule to complement the −4 charge on the octamolybdate anion. The α-phase Keggin-type anion in 2, [PMoVMo11O40]4−, contains one Mo atom in the +5 oxidation state, indicating that 2 is a charge transfer complex. The α-phase Keggin-type anion in 3, [PMo12O40]3−, has 12 fully-oxidized Mo atoms. Compound 3 has a band gap ∼3.5 eV. The catalytic nature of compound 3 in the oxidation of styrene to benzaldehyde was investigated. The maximum styrene conversion was 83%, while the maximum selectivity to benzaldehyde was 96.5%. The catalyst was successfully used for five cycles without significant loss in activity or selectivity. The structure of the catalyst remains unchanged after repeated use. Our work points to the feasibility of generating a wide variety of new and useful POM-based compounds through a ‘green’ synthesis route.

Hydrophobic and Metallophobic Surfaces: Highly Stable Non-wetting Inorganic Surfaces Based on Lanthanum Phosphate Nanorods.

Metal oxides, in general, are known to exhibit significant wettability towards water molecules because of the high feasibility of synergetic hydrogen-bonding interactions possible at the solid-water interface. Here we show that the nano sized phosphates of rare earth materials (Rare Earth Phosphates, REPs), LaPO4 in particular, exhibit without any chemical modification, unique combination of intrinsic properties including remarkable hydrophobicity that could be retained even after exposure to extreme temperatures and harsh hydrothermal conditions. Transparent nanocoatings of LaPO4 as well as mixture of other REPs on glass surfaces are shown to display notable hydrophobicity with water contact angle (WCA) value of 120° while sintered and polished monoliths manifested WCA greater than 105°. Significantly, these materials in the form of coatings and monoliths also exhibit complete non-wettability and inertness towards molten metals like Ag, Zn, and Al well above their melting points. These properties, coupled with their excellent chemical and thermal stability, ease of processing, machinability and their versatile photo-physical and emission properties, render LaPO4 and other REP ceramics utility in diverse applications.

Solvent effects on some new meso-aryl substituted octabromoporphyrins

A series of porphyrins with tolyl and naphthyl substituents at themeso positions, their octabromoderivatives (OBP) with Br substituents at β-pyrrole positions are synthesised and characterised by chemical analysis,1H NMR and electronic spectral studies. It is seen that all the OBPs exhibit pronounced red shifts in both the Soret andQ bands of their electronic spectra compared to their non-brominated form in various polar and nonpolar solvents, the energy difference Δv being in the range 2300–2700 cm−1. The high energyB band of naphthyl porphyrins (both brominated and nonbrominated) are found to be more red-shifted than that of tolyl porphyrins, owing to the noticeable mesomeric effect of the naphthyl groups. Detailed spectral studies reveal that while none of the nonbrominated porphyrin show solvent-dependent change in theirB andQ bands, all the OBPs manifest significant shifts depending on the nature of solvents. Solvent-solute interaction can be considered to be of strong dipole-dipole nature for OBPs with polar solvents and of π-π type with aromatic non-polar solvents. In the brominated form we find two categories of porphyrins exhibiting distinctly different absorption phenomena in aromatic solvents. The OBPs havingmeso-groups not shielding the porphyrin π-framework exhibit additional absorption peaks (split Soret peaks and broadened Q bands) in some aromatic solvents. This could be explained in terms of π-π type donor-acceptor (DA) complex formation between such bromoporphyrins (acceptor) and the aromatic solvent molecules (donor) that is not possible for OBPs that have bulkymeso groups that block the approach of aromatic solvent molecules close to the porphyrin framework

Studies on iron(III) and manganese(III) derivatives of new meso-aryl substituted and brominated porphyrins

A series of FeIII and MnIII porphyrins with various tolyl and naphthyl substituents at the meso positions, and their perbromoderivatives with Br substituents at the β-pyrrole positions, have been synthesised and investigated. As seen in the case of the free-base porphyrins, both FeIII and MnIII derivatives of the Br-substituted porphyrins also exhibit pronounced red-shifts in both B and Q bands compared to their nonbrominated analogues. This is attributed to the electron-withdrawing ability of eight Br substituents at β-pyrrole positions and is also due to distortion brought about in the π-framework by the bulky substituents including those at the meso positions. The naphthyl groups seem to be making mesomeric contributions for both nonbrominated and brominated porphyrins of these metal ions as is evident from the higher wavelength absorption of the B band as compared to the tolyl derivatives. While the meso-substituent do not exhibit any isomer dependent change on the electronic properties of FeIII porphyrins, they show a noticeable effect in the MnIII derivatives. During the metallation of meso-tetratolylporphyrins by FeIII ions μ-oxo dimeric compounds are formed, while the naphthyl porphyrins and the bromoderivatives do not form such dimeric species. The presence of bulky groups at the meso positions and heavy bromines on the β-pyrrole positions can be considered to prevent the formation of catalytically inert μ-oxo dimers.

Sol-Gel Lanthanum Phosphate: A Versatile Ceramic Material for Diverse Functional Applications

Lanthanum phosphate (LaPO4) is one among the lanthanide family of rare earth phosphates characterized by versatile properties such as hydrophobicity, metallophobicity, low thermal conductivity and machinability. The possibility of creating non-wetting inorganic surfaces by simple wet chemical coating approaches impart diverse functionality to this material and a host of applications ranging from hydrophobic surfaces to metallophobic surfaces at T–1100 °C are realized. This chapter gives an overview of lanthanum phosphate ceramics and includes a detailed case study on the synthesis, morphology and phase formation of lanthanum phosphate nano-composites using a Sol-Gel approach and its application as coatings and monoliths for a variety of functional applications.

Structural and magnetic properties of spin-

We present the synthesis and a detailed investigation of structural and magnetic properties of metal-organic compound Cu2(IPA)2(DMF)(H2O) by means of x-ray diffraction, magnetization, and heat capacity measurements. Single crystals of the title compound were synthesized by judicious selection of organic ligand and employing a selective hydrothermal reaction route. It crystallizes in an orthorhombic structure with space group Cmca. The structural analysis revealed that two Cu2+ ions are held together by the organic component (-O-C-O-) in a square paddle-wheel to form spin dimers which are aligned perpendicular to each other and are further coupled through organic ligands (isophthalic acid) forming two-dimensional layers. Temperature dependent magnetic susceptibility [Formula: see text] could be described well using spin-1/2 dimer model. The spin susceptibility [Formula: see text] shows an exponential decrease in the low temperature region, below the broad maximum, confirming the singlet ground state with a large spin gap of [Formula: see text] K. The heat capacity C p measured as a function of temperature also confirms the absence of magnetic long-range-order down to 2 K.We present the synthesis and a detailed investigation of structural and magnetic properties of metal-organic compound Cu

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