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      Volume 122, Issue 1

      January 2010,   pages  5-89

    • Foreword

      D Das V K Jain

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    • Multidimensional potential of boron-containing molecules in functional materials

      Wolfgang Kaim Narayan S Hosmane

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      Boron-containing molecular systems have received much attention under theoretical aspects and from the side of synthetic organic chemistry. However, their potential for further applications such as optically interesting effects such as Non-Linear Optics (NLO), medical uses for Boron Neutron Capture Therapy (BNCT), or magnetism has been recognised only fairly recently. Molecular systems containing boron offer particular mechanisms to accommodate unpaired electrons which may result in stable radicals as spin-bearing materials. Among such materials are organoboron compounds in which the prototypical electron deficient (10B, 11B) boron vs. carbon centers can accept and help to delocalise added electrons in a 2-dimensionally conjugated 𝜋 system. Alternatively, oligoboron clusters B$_n$X$_n^k$ and the related carboranes or metallacarboranes are capable of adding or losing single electrons to form paramagnetic clusters with 3-dimensionally delocalised spin, according to combined experimental studies and quantum chemical calculations. The unique nuclear properties of 10B are of therapeutic value if their selective transport via appended carbon nanotubes, boron nanotubes, or magnetic nanoparticles can be effected.

    • Magnetic behaviour in metal-organic frameworks — Some recent examples

      Partha Mahata Debajit Sarma Srinivasan Natarajan

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      The article describes the synthesis, structure and magnetic investigations of a series of metal-organic framework compounds formed with Mn+2 and Ni+2 ions. The structures, determined using the single crystal X-ray diffraction, indicated that the structures possess two- and three-dimensional structures with magnetically active dimers, tetramers, chains, two-dimensional layers connected by polycarboxylic acids. These compounds provide good examples for the investigations of magnetic behaviour. Magnetic studies have been carried out using SQUID magnetometer in the range of 2-300 K and the behaviour indicates a predominant anti-ferromagnetic interactions, which appears to differ based on the M-O-C-O-M and/or the M-O-M (M = metal ions) linkages. Thus, compounds with carboxylate (Mn- O-C-O-Mn) connected ones, [C3N2H5][Mn(H2O){C6H3(COO)3\}], I, [{Mn(H2O)3}{C12H8O(COO)2}]$\cdots$H2O, II, [{Mn(H2O)}{C12H8O(COO)2}], III, show simple anti-ferromagnetic behaviour. The compounds with Mn-O/OH-Mn connected dimer and tetramer units in [NaMn{C6H3(COO)3}], IV, [Mn2($\mu_3$-OH) (H2O)2{C6H3(COO)3}]$\cdot$2H2O, V, show canted-antiferromagnetic and anti-ferromagnetic behaviour, respectively. The presence of infinite one-dimensional -Ni-OH-Ni- chains in the compound, [NiR_2R(HR_2RO)($\mu_3$-OH)2(C8H5NO4], VI, gives rise to ferromagnet-like behaviour at low temperatures. The compounds, [Mn3{C6H3(COO)3}$2], VII and [{Mn(OH)}2{C12H8O(COO)2}], VIII, have two-dimensional infinite -Mn-O/OH-Mn- layers with triangular magnetic lattices, which resemble the Kagome and brucite-like layer. The magnetic studies indicated canted-antiferromagnetic behaviour in both the cases. Variable temperature EPR and theoretical magnetic modelling studies have been carried out on selected compounds to probe the nature of the magnetic species and their interactions with them.

    • Synthesis, structure and electrical conductivity of fulvalenium salts of cobalt bis(dicarbollide) anion and its derivatives

      Vladimir Bregadze Igor Sivaev Irina Lobanova Olga Kazheva Grigorii Alexandrov Andrey Kravchenko Vladimir Starodub Lev Buravov Lev Titov Oleg Dyachenko

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      TTF, TTF-BMDT, TTF-BEDT and TMTSF cation radical salts of cobalt bis(dicarbollide) anion [3,3'-Co(1,2-C2B9H11)2]- and its derivatives are prepared and their crystal structures and electrical conductivities are determined. Some regularities in the crystal structures of the TTF-based radical cation salts prepared are also discussed.

    • Superconductivity at 31.3 K in Yb-doped La(O/F)FeAs superconductors

      J Prakash S J Singh S Patnaik A K Ganguli

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      The effect of ytterbium substitution at the lanthanum site on the superconducting properties of La$_{1-x}$Yb$_x$O0.8F0.2FeAs ($x = 0.10$, 0.20 and 0.30) oxypnictides has been investigated. Powder X-ray diffraction studies show the presence of Yb2O3 and LaOF as secondary phases. The superconducting transition temperature ($T_c$) of 31.3 ($\pm \, 0.05$) K has been observed in $x = 0.1$ composition which is the maximum $T_c$ so far in the La(O/F)FeAs superconductor family at ambient pressure. Further increase in 𝑥 leads to suppression and broadening of superconducting transition. The resistive transition curves under different magnetic fields were investigated, leading to determination of upper critical field $H_{c2}$ (𝑇) of this new superconductor. The value of $H_{c2}$ at zero temperature is estimated to be about 46 T corresponding to coherence length ∼ 27 Å.

    • Molecular tailoring approach for exploring structures, energetics and properties of clusters

      Shridhar R Gadre K V Jovan Jose Anuja P Rahalkar

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      Molecular Tailoring Approach (MTA) is a method developed for enabling ab initio calculations on prohibitively large molecules or atomic/molecular clusters. A brief review of MTA, a linear scaling technique based on set inclusion and exclusion principle, is provided. The Molecular Electrostatic Potential (MESP) of smaller clusters is exploited for building initial geometries for the larger ones, followed by MTA geometry optimization. The applications of MTA are illustrated with a few test cases such as (CO2)$_n$ and Li$_n$ clusters employing Density Functional theory (DFT) and a nanocluster of orthoboric acid at the Hartree-Fock (HF) level. Further, a discussion on the geometries and energetics of benzene tetramers and pentamers, treated at the Møller-Plesset second order (MP2) perturbation theory, is given. MTA model is employed for evaluating some cluster properties viz. adiabatic ionization potential, MESP, polarizability, Hessian matrix and infrared frequencies. These property evaluations are carried out on a series of test cases and are seen to offer quite good agreement with those computed by an actual calculation. These case studies highlight the advantages of MTA model calculations vis-à-vis the actual ones with reference to the CPU-time, memory requirements and accuracy.

    • Development of gas sensors using ZnO nanostructures

      S K Gupta Aditee Joshi Manmeet Kaur

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      Different ZnO nanostructures such as nanowires, nanobelts and tetrapods have been grown and used for preparation of thick film (with random grain boundaries) as well as isolated nanowire/nanobelt gas sensors. Sensitivity of different type of sensors has been studied to H2S and NO gases. The results show that the response of ZnO sensors to H2S arises from grain boundary only whereas both grain boundaries and intragrain resistances contribute towards response to NO. In addition, oxygen vacancies in the lattice were also seen to help in improvement of sensor response. Room temperature operating H2S and NO sensors based on ZnO nanowires have been demonstrated. Further, sensors based on isolated nanobelts were found to be highly selective in their response to NO.

    • One-pot, three-component synthesis of highly substituted pyridines and 1,4-dihydropyridines by using nanocrystalline magnesium oxide

      M Lakshmi Kantam Koosam Mahendar Suresh Bhargava

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      One pot, three component synthesis of 2-amino-4-aryl-3,5-dicyano-6-sulfanylpyridines and the corresponding 1,4-dihydropyridines are from readily accessible starting materials is described. Simply heating of an ethanolic solution of structurally diverse aldehydes with various thiols and malononitrile in the presence of nanocrystalline magnesium oxide provides the highly substituted pyridine derivatives in moderate to high yields, each representing a privileged medicinal scaffold with their structural motif. After completion of the reaction, the catalyst can be recovered efficiently and reused with constintent activity.

    • Microwave-assisted low temperature synthesis of sodium zirconium phosphate (NZP) and the leachability of some selected fission products incorporated in its structure - A case study of leachability of cesium

      A H Naik S B Deb A B Chalke M K Saxena K L Ramakumar V Venugopal S R Dharwadkar

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      Microwave-assisted procedure for low temperature solid state synthesis of sodium zirconium phosphate (NZP), a material with the potential for immobilization and disposal of high level nuclear waste, was developed. Three selected fission products, namely, Cesium, Strontium and Tellurium were introduced (substituted) in the NZP matrix during its synthesis at 450°C. Leaching studies were carried out on the fission product substituted NZP sintered at 1000°C, in pure de-ionized water and 80% saturated brine solution at the ambient temperatures of 30°C and 90°C for four weeks. The major part of leaching in all the cases was observed in the first week. The extent of leaching after four weeks was found not exceeded from 12 to 15% of the elements substituted in NZP, which later became negligibly small. The effect of temperature and the nature of leachant on the leaching rate did not indicate any systematic trend. The EDX analysis of the surfaces of the leached NZP pellets showed that the leaching of the dopants is limited mainly to the surface region of the sintered pellets.

    • Kinetics of solid state phase transformations: Measurement and modelling of some basic issues

      S Raju E Mohandas

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      A brief review of the issues involved in modelling of the solid state transformation kinetics is presented. The fact that apart from the standard thermodynamic parameters, certain path variables like heating or cooling rate can also exert a crucial influence on the kinetic outcome is stressed. The kinetic specialties that are intrinsic to phase changes proceeding under varying thermal history are enumerated. A simple and general modelling methodology for understanding the kinetics of non-isothermal transformations is outlined.

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