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      Volume 131, Issue 11

      November 2019

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    • Structure-dependence of electrical conductivity and electrocatalytic properties of Sr2 Mn22 O6 and CaSrMn2O6

      RAM KRISHNA HONA FARSHID RAMEZANIPOUR

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      Remarkable enhancement of the electrical conductivity and electrocatalytic activity is demon-strated as a result of the transformation of crystal structure between Sr2 Mn2 O6 and CaSrMn2O6. The structure of Sr2 Mn2O6 is known to consist of dimeric units of face-sharing MnO6 octahedra. Whereas, CaSrMn2 O6 contains individual octahedra, connected to each other through corner-sharing. Herein we show that the changes in the crystal structure result in significant improvement of the electrical conductivity, by five orders of magnitude, for CaSrMn2O6 compared to Sr2 Mn2 O6. Variable temperature conductivity studies from 25–800°C indicate semiconducting properties for both compounds, where the enhanced conductivity of CaSrMn2 O6 persists in the entire temperature range. The electrocatalytic activity of both compounds toward oxygen evolution reaction (OER) has also been investigated, indicating superior OER activity of CaSrMn2O6 compared to Sr2 Mn2 O6 . A pronounced improvement in the onset potential and kinetics of OER is observed for CaSrMn2 O6 . These studies demonstrate an important correlation between crystal structure, electrical conductivity and electrocatalytic properties

    • DFT studies on the structure and stability of tetraaza macrocyclic nickel(II) complexes containing dicarbinolamine ligand moiety

      E J PADMA MALAR REBECCA JACOB S BALASUBRAMANIAN

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      Density functional theory calculations at M052X/6-311++ G** level were performed to under-stand the structure and stability of Ni(II) tetraaza macrocyclicdicarbinolamine complex 1. The preferentialstability of 1 over the hitherto unknown Ni(II) complex having fully conjugated macrocyclic ligand 2,is examined by analyzing geometric and electronic structures and energy considerations. The present calcula-tions predict that in the trans (C2) structure, 1 is 102 kcal/mol more stable than its components 2 and 2(OH) at M062X-D3/def2-QZVP//M052X/6-311++ G** level. This significant stabilization explains the formation of 1 as experimentally observed. The calculations support a distorted square planar environment for Ni in 1,inagreement with the observed spectral and magnetic properties. In order to understand the stability of 1 ,weexamined the second-order stabilizing interactions in natural bond orbital (NBO) basis, the role of the noncovalent dispersion energy, macrocyclic cavity size, Ni-ligand covalent bond strength, natural electronic population on the atomic centers and the nature of the frontier molecular orbitals in the complexes. The present study reveals that the higher stability of 1 over 2 is primarily due to the stronger covalent bonds between the Ni(II) centre, and two of the coordinating nitrogen atoms in 1 than in 2 and significant second-order stabilizing interactions originating from the NBOs involving the oxygen atoms

    • Palladium nanoparticles supported on fluorine-doped tin oxide as an efficient heterogeneous catalyst for Suzuki coupling and 4-nitrophenol reduction

      SEK YIN MAK KIN HONG LIEW CHIA CHIA CHUA MOHD AMBAR YARMO BADRUL H YAHAYA WAN ZURINA SAMAD MOHD SUZEREN MD JAMIL RAHIMI M YUSOP

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      Immobilization of palladium nanoparticles onto the fluorine-doped tin oxide (FTO) as support Pd/FTO, resulted in a highly active heterogeneous catalyst for Suzuki-Miyaura cross-coupling reactions and 4-nitrophenol reduction. The Pd/FTO catalyst has been synthesized by immobilization of palladium nanoparticles onto FTO via a simple impregnation method. ICP-MS analysis confirmed that there is 0.11 mmol/g of palladium was loaded successfully on FTO support. The crystallinity, morphologies, com-positions and surface properties of Pd/FTO were fully characterized by various techniques. It was further examined for its catalytic activity and robustness in Suzuki coupling reaction with different aryl halides andsolvents. The yields obtained from Suzuki coupling reactions were basically over 80%. The prepared catalyst was also tested on mild reaction such as reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). Pd/FTO catalyst exhibited high catalytic activity towards 4-NP reduction with a rate constant of 1.776 min-1 and turnover frequency (TOF) value of 29.1 hr-1. The findings revealed that Pd/FTO also maintained its high stability for five consecutive runs in Suzuki reactions and 4-NP reductions. The catalyst showed excellent catalytic activities by using a small amount of Pd/FTO for the Suzuki coupling reaction and 4-NP reduction.

    • Nickel-zinc hydroxy salts with varying amounts of octahedral Zn2+ : trends in stability and selectivity in anion exchange reaction

      MIKHAIL RAJARAM KOLINJAVADI BHOJARAJ MICHAEL RAJAMATHI

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      Nickel-zinc hydroxy acetates with varying amounts of octahedral zinc, Ni(3-x)Zn((3-x)(OH)8(OAc)2.mH2 O, with x varying from 0 to 2, have been synthesized. The crystallographic 'a' parameter increases linearly with octahedral zinc content in the series. While the thermal stability is almost the same for the entire series of compounds, the stability of the compound in the alkaline medium increases with a decrease in octahedral zinc content. The selectivity for chloride ion from a mixture of chloride and bromide ions increases linearly with an increase in octahedral zinc content.

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