Rabindranath Mukherjee

Indian Institute of Technology Kanpur, Cawnpore, Uttar Pradesh, India

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Publications (108)339.17 Total impact

  • Akram Ali · Suman K Barman · Rabindranath Mukherjee
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    ABSTRACT: A new potentially tetradentate redox-active o-aminophenol-based ligand, H2L = 2-(2-ethylthio)pyridine-anilino-4,6-di-tert-butylphenol, reacts with Pd(II)(O2CCH3)2 in CH3OH in the presence of air and Et3N affording isolation of a green crystalline solid of composition [Pd(L)] 1. When examined by cyclic voltammetry (CV), 1 exhibits two quasireversible oxidative responses at E1/2 = 0.16 (peak-to-peak separation, ΔEp = 100 mV) and 0.89 V (ΔEp = 90 mV) vs SCE (saturated calomel electrode). Chemical oxidation of 1 by [Fe(III)(η(5)-C5H5)2][PF6] and AgBF4 in CH2Cl2 led to the isolation of two crystalline solids, red [Pd(L)][PF6]·CH2Cl2 2 and dark green [Pd(L)][BF4]2·2CH2Cl2 3, respectively. Single-crystal X-ray crystallography at 100(2) K unambiguously established that the O,N,S,N-coordinated ligand is present in the square-planar complexes [Pd(II){(L(AP))(2-)}] 1, [Pd(II){(L(ISQ))(•-)}][PF6]·CH2Cl2 2, and [Pd(II){(L(IBQ))(0)}][BF4]2·2CH2Cl2 3, as dianionic (L(AP))(2-), monoanionic o-iminobenzosemiquinonate(1-) π-radical (Srad = (1)/2) (L(ISQ))(•-), and neutral o-iminobenzoquinone (L(IBQ))(0) redox level. Reaction of 1 and 2 with PPh3 afforded isolation of two crystalline complexes: dark green [Pd(II)(L)(PPh3)] 4 and red [Pd(II){(L(ISQ))(•-)}(PPh3)][PF6]·CH2Cl2 5. X-ray structure determination of 5 at 100(2) K revealed Pd(II)ON2P coordination environment. The square-planar complexes 1-5 possess an S = 0, (1)/2, 0, 0, and (1)/2 ground-state, respectively, as was established by (1)H NMR and EPR spectroscopy, and room-temperature magnetic moment data. All redox processes are thus shown to be ligand-based. Absorption spectral measurements were done for all complexes. DFT calculations at B3LYP-level of theory adequately describe the electronic structures of 1-3, and 5, containing a spin-paired d(8) Pd(II) ion. Time-dependent-DFT calculations on 1-3 and 5 shed light on the origin of UV-vis-NIR spectral absorptions.
    No preview · Article · May 2015 · Inorganic Chemistry
  • Vibha Mishra · Anuj Kumar Sharma · Rabindranath Mukherjee
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    ABSTRACT: Reaction of 2-[3-(2′-pyridyl)pyrazol-1-ylmethyl](1-methylimidazole) (L3) with ZnCl2 affords [(L3)ZnIICl2] 1. Crystal structure analysis of 1 reveals that the ZnII ion assumes a slightly distorted square-pyramidal geometry with coordination by the tridentate nonplanar ligand L3, providing a pyridine, a pyrazole and an imidazole N donors and two chloride ions. Notably, secondary interactions [C–H⋯Cl (–CH2– hydrogen of the spacer and –CH3 hydrogen of 1-methylimidazole)] triggered by ZnII-coordinated chloride ions acting as hydrogen-bonding acceptors generates self-complementary dimeric tectons, which lead to 1D supramolecular chain.
    No preview · Article · Jun 2014 · Proceedings of the National Academy of Sciences, India - Section A
  • Ravindra Singh · Francesc Lloret · Rabindranath Mukherjee
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    ABSTRACT: The synthesis, structural characterization, and magnetic properties of three copper(II) complexes, a mono-chloro-bridged [Cu2II(L6)2(μ-Cl)(Cl)(CuIICl4)] (1) and a dichloro-bridged [CuII2(L7)2(μ-Cl)2][ClO4]2 (3) discrete trimers and dimers, and a mono-chloro-bridged 1D-coordination polymer [CuII(L6)(μ-Cl)][ClO4]·CH3CN (2), are reported. Molecular structures were authenticated by X-ray crystallography. Temperature-dependent magnetic measurements carried out on powdered samples of 1–3 indicated a very weak antiferromagnetic exchange-coupling within the {CuII(μ-Cl)CuII(μ-Cl)CuIICl3}+ units in 1 [Curie-Weiss plot: θ = –0.19(1) K and g = 2.07(1)], a ferromagnetic behavior within {CuII(μ-Cl)2CuII}2+ units in 3 [Ĥ = –JS1·S2: J = +6.0(1) cm–1, D (zero-field splitting parameter) = 4.5(2) cm–1, and g = 2.11], and a weak intrachain antiferromagnetic behavior due to {CuII(μ-Cl)CuII}3+ units in 2 [single-chain polymer: J = –0.20(1) cm–1 and g = 2.11]. The square-pyramidal stereochemistry of the central copper(II) atoms in 1–3 was identified by their absorption spectral properties in acetontrile. An attempt was made to rationalize the observed magneto-structural behavior.
    No preview · Article · Mar 2014 · Zeitschrift für anorganische Chemie
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    Amit Rajput · Anuj K Sharma · Suman K Barman · Debasis Koley · Markus Steinert · Rabindranath Mukherjee
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    ABSTRACT: A brownish-black complex [Fe(III)(L)2] (1) (S = 0), supported by two tridentate redox-active azo-appended o-amidophenolates [H2L = 2-(2-phenylazo)-anilino-4,6-di-tert-butylphenol], has been synthesized and structurally characterized. In CH2Cl2 1 displays two oxidative and two reductive 1e(-) redox processes at E1/2 values of 0.48 and 1.06 V and -0.42 and -1.48 V vs SCE, respectively. The one-electron oxidized form [1](+) isolated as a green solid [Fe(III)(L)2][BF4] (2) (S = 1/2) has been structurally characterized. Isolation of a dark ink-blue one-electron reduced form [1](-) has also been achieved [Co(III)(η(5)-C10H15)2][Fe(III)(L)2] (3) (S = 1/2). Mössbauer spectral parameters unequivocally establish that 1 is a low-spin (LS) Fe(III) complex. Careful analysis of Mössbauer spectral data of 2 and 3 at 200 and 80 K reveal that each complex has a major LS Fe(III) and a minor LS Fe(II) component (redox isomers): [Fe(III){(L(ISQ))(-•)}2](+) and [Fe(II){(L(IBQ))(0)}{(L(ISQ))(-•)}](+) (2) and [Fe(III){(L(AP))(2-)}2](-) and [Fe(II){(L(ISQ))(-•)}{(L(AP))(2-)}](-) (3). Notably, for both at 8 K mainly the major component exists. Broken-Symmetry (BS) Density Functional Theory (DFT) calculations at the B3LYP level reveals that in 1 the unpaired electron of LS Fe(III) is strongly antiferromagnetically coupled with a π-radical of o-iminobenzosemiquinonate(1-) (L(ISQ))(-•) form of the ligand, delocalized over two ligands providing 3- charge (X-ray structure). DFT calculations reveal that the unpaired electron in 2 is due to (L(ISQ))(-•) [LS Fe(III) (SFe = 1/2) is strongly antiferromagnetically coupled to one of the (L(ISQ))(-•) radicals (Srad = 1/2)] and 3 is primarily a LS Fe(III) complex, supported by two o-amidophenolate(2-) ligands. Time-Dependent-DFT calculations shed light on the origin of UV-vis-NIR spectral absorptions for 1-3. The collective consideration of Mössbauer, variable-temperature (77-298 K) electron paramagnetic resonance (EPR), and absorption spectral behavior at 298 K, and DFT results reveals that in 2 and 3 the valence-tautomerism is operative in the temperature range 80-300 K.
    Preview · Article · Jan 2014 · Inorganic Chemistry
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    ABSTRACT: The dinuclear complex [Zn2(DPCPMP)(pivalate)](ClO4), where DPCPMP is the new unsymmetrical ligand [2-(N-(3-((bis((pyridin-2-yl)methyl)amino)methyl)-2-hydroxy-5-methylbenzyl)-N-((pyridin-2-yl)methyl)amino)acetic acid], has been synthesized and characterized. The complex is a functional model for zinc phosphoesterases with dinuclear active sites. The hydrolytic efficacy of the complex has been investigated using bis-(2,4-dinitrophenyl)phosphate (BDNPP), a DNA analog, as substrate. Speciation studies using potentiometric titrations have been performed for both the ligand and the corresponding dizinc complex to elucidate the formation of the active hydrolysis catalyst; it reveals that the dinuclear zinc(II) complexes, [Zn2(DPCPMP)](2+) and [Zn2(DPCPMP)(OH)](+) predominate the solution above pH4. The relatively high pKa of 8.38 for water deprotonation suggests that a terminal hydroxide complex is formed. Kinetic investigations of BDNPP hydrolysis over the pH range 5.5-11.0 and with varying metal to ligand ratio (metal salt:ligand=0.5:1 to 3:1) have been performed. Variable temperature studies gave the activation parameters ΔH(‡)=95.59kJmol(-1), ΔS(‡)=-44.82Jmol(-1)K(-1), and ΔG(‡)=108.00kJmol(-1). The cumulative results indicate the hydroxido-bridged dinuclear Zn(II) complex [Zn2(DPCPMP)(μ-OH)](+) as the effective catalyst. The mechanism of hydrolysis has been probed by computational modeling using density functional theory (DFT). Calculations show that the reaction goes through one concerted step (SN2 type) in which the bridging hydroxide in the transition state becomes terminal and performs a nucleophilic attack on the BDNPP phosphorus; leaving group dissociates simultaneously in an overall inner sphere type activation. Calculated free energy barrier is in good agreement with the experimentally determined activation parameters.
    Full-text · Article · Aug 2013 · Journal of inorganic biochemistry
  • Anuj Kumar Sharma · Francesc Lloret · Rabindranath Mukherjee
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    ABSTRACT: A full report on the synthesis, crystal structure, spectroscopic characterization, and magnetic properties of two new trinuclear complexes (one homo- and another heterotrinuclear) [(L)2Co(II)3(OAc)4(MeOH)2]·6MeOH (1) and [(L)2Co(II)2Mn(II)(OAc)4(MeOH)2]·6MeOH (2) [HL = N-methyl-N-2-hydroxybenzyl-2-aminoethyl-2-pyridine] is presented. The properties of 1 and 2 are compared to that of three previously communicated complexes [(L)2Ni(II)3(OAc)4(MeOH)2]·6MeOH (3), [(L)2Ni(II)2Mn(II)(OAc)4(H2O)2] (4), and [(L)2Ni(II)2Co(II)(OAc)4(MeOH)2]·6MeOH (5) (Inorg. Chem.2007, 46, 5128-5130). All are centrosymmetric trimers with the central metal ion situated on an inversion center. Adjacent metal ions are triply bridged by a μ2-phenolate and two acetate (one in μ2-1,1 mode and another in μ2-1,3 mode) groups. Magnetic investigations reveal that the complexes are ferromagnetically coupled (J in cm(-1)): +1.20 (1) and +0.71 (2). The reported J values are +1.10 (3), -0.30 (4), and +1.06 (5). It reveals that total spins are as follows: S = 9/2 (1), 11/2 (2), 3 (3), 1/2 (4), 7/2 (5). The role of M-O(μ2-phenoxide)-M', M-O(μ2-1,1-acetate)-M', and M-O(μ2-1,3-acetate)-M' (M = M' = Co(II), Ni(II); M = Co(II), M' = Mn(II); M = Ni(II), M' = Mn(II), Co(II)) bond angles on the observed magnetic behavior has been noted.
    No preview · Article · Apr 2013 · Inorganic Chemistry
  • Amit Rajput · Rabindranath Mukherjee
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    ABSTRACT: Pyridine-2-carboxamide and pyridine-2,6-dicarboxamide-based chelating ligands form a variety of coordination complexes with a number of metal ions, providing varying coordination geometry and nuclearity. Recent years have seen considerable interest in the designing of this class of ligands and to study their structural properties to serve specific stereochemical requirement of a particular metal-binding site. Notably, this class of ligands has been extensively utilized by Mascharak and co-workers to provide low-molecular-weight representations of metallo-proteins/enzymes such as bleomycins, nitrile hydratase. Moreover, the transition metal complexes of this class of ligands are being used as various exogenous nitric oxide (NO) donors. Using over 60 this class of chelating carboxamide ligands, the stereochemical properties of over 150 discrete coordination complexes, studied by single-crystal X-ray crystallography have been analyzed. Various bonding modes for a given chelating ligand are involved, and are reviewed with reference to ligand structure and the resulting coordination complexes. It is shown that the complexes synthesized have served to address notable issues such as effect of ligand structure/donor atom on metal-centered redox potentials, change of spin-state of iron(III), ligand-radical coordinated metal-complexes, interesting chemical reactivity studies, and catalytic potential. The ligands are introduced systematically as a function of their denticity, making easy access to information on specific type of ligands and coordination complexes thereof. X-ray crystallographically determined bond lengths of various donor atoms/groups are collected in a table, thus providing an accessible source for reference purposes. Source material for the review amounts to about 90 references.
    No preview · Article · Jan 2013 · Coordination Chemistry Reviews
  • Sukanta Mandal · Jhumpa Mukherjee · Francesc Lloret · Rabindranath Mukherjee
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    ABSTRACT: Chemical model systems possessing the reactivity aspects of both tyrosinase and catechol oxidase are presented. Using two m-xylyl-based ligands providing bidentate alkylamine terminal coordination, 1,3-bis[(N,N-dimethylaminoethyl)aminomethyl]benzene (L(H,H)) and 1,3-bis[(N,N,N'-trimethylaminoethyl)aminomethyl]benzene (L(Me,Me)), four new dicopper(I) complexes, [Cu(I)(2)(L(H,H))(MeCN)(4)][ClO(4)](2) (1), [Cu(I)(2)(L(H,H))(PPh(3))(2)(MeCN)(2)][ClO(4)](2) (2), [Cu(I)(2)(L(Me,Me))(MeCN)(2)][ClO(4)](2) (3), and [Cu(I)(2)(L(Me,Me))(PPh(3))(2)][ClO(4)](2) (4), have been synthesized and characterized. Complex 2 has been structurally characterized. Reaction of the dicopper(I) complex 3(2+) with dioxygen at 183 K generates putative bis(μ-oxo)dicopper(III) intermediate (absorption spectroscopy). Oxygenation of 1 and 3 brings about m-xylyl-ring hydroxylation (monooxygenase-like activity), with a noticeable color change from pale-yellow to dark green. The presence of phenoxo- and hydroxo-bridges in the end products [Cu(II)(2)(L(H,H)-O)(OH)(MeCN)(2)][ClO(4)](2) (5) and [Cu(II)(2)(L(Me,Me)-O)(OH)(OClO(3))][ClO(4)]·MeCN(6) has been authenticated by structural characterization. Oxygenation of 3 afforded not only the green complex 6 isolation but also a blue complex [Cu(II)(2)(L(Me,Me))(OH)(2)][ClO(4)](2) (7). Variable temperature magnetic susceptibility measurements on 5 and 6 establish that the Cu(II) centers are strongly antiferromagnetically coupled [singlet-triplet energy gap (J) = -528 cm(-1) (5) and -505 cm(-1) (6)]. The abilities of phenoxo- and hydroxo-bridged dicopper(II) complexes 5 and 6, the previously reported complex [Cu(II)(2)(L(1)-O)(OH)(OClO(3))(2)]·1.5H(2)O (8) (L(1)-OH = 1,3-bis[(2-dimethylaminoethyl)iminomethyl]phenol), and [Cu(II)(2)(L(2)-O)(OH)(OClO(3))()][ClO(4)]() (9) (L(2)-OH = 1,3-[(2-dimethylaminoethyl)iminomethyl][(N,N,N'-trimethyl)aminoethyl]-4-methylphenol) have been examined to catalyze the oxidation of catechol to quinone (catecholase activity of tyrosinase and catechol oxidase-like activity) by employing the model substrate 3,5-di-tert-butylcatechol. Saturation kinetic studies have been performed on these systems to arrive at the following reactivity order [k(cat)/K(M) (catalytic efficiency) × 10(-3) (M(-1) h(-1))]: 470 (6) > 367 (5) > 128 (9) > 90 (8).
    No preview · Article · Nov 2012 · Inorganic Chemistry
  • Himanshu Arora · Suman K Barman · Francesc Lloret · Rabindranath Mukherjee
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    ABSTRACT: The six phenoxo- and bis(acetato)-bridged dimetal(II) complexes [MII2(L2)(μ-O2CMe)2(MeCN)2][PF6] (M = Mn (2a), Co (3a), Zn (4a)) and [MII2(L2)(μ-O2CMe)2(MeCN)2][BPh4]·2MeCN (M = Mn (2b·2MeCN), Co (3b·2MeCN), Zn (4b·2MeCN)) have been synthesized, and their physicochemical (2a,b, 3a,b, and 4a,b) and magnetic properties (2b and 3b) have been studied and compared. Complexes 2b·2MeCN, 3b·2MeCN, and 4b·2MeCN have been structurally characterized. From the viewpoint of a functional model study of binuclear metallophosphatases the hydrolysis/transesterification of 2-hydroxypropyl-p-nitrophenylphosphate (HPNP) by complexes 2a−4a in MeOH/H2O (30%, v/v), having labile coordination sites to generate an MII-bound hydroxide ion as the nucleophile, has been investigated.
    No preview · Article · Apr 2012 · Inorganic Chemistry
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    Sharmila Pandey · Partha Pratim Das · Akhilesh Kumar Singh · Rabindranath Mukherjee
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    ABSTRACT: Using an acyclic hexadentate pyridine amide ligand, containing a -OCH(2)CH(2)O- spacer between two pyridine-2-carboxamide units (1,4-bis[o-(pyrydine-2-carboxamidophenyl)]-1,4-dioxabutane (H(2)L(9)), in its deprotonated form), four new complexes, [Co(II)(L(9))] (1) and its one-electron oxidized counterpart [Co(III)(L(9))][NO(3)]·2H(2)O (2), [Ni(II)(L(9))] (3) and [Cu(II)(L(9))] (4), have been synthesized. Structural analyses revealed that the Co(II) centre in 1 and the Ni(II) centre in 3 are six-coordinate, utilizing all the available donor sites and the Cu(II) centre in 4 is effectively five-coordinated (one of the ether O atoms does not participate in coordination). The structural parameters associated with the change in the metal coordination environment have been compared with corresponding complexes of thioether-containing hexadentate ligands. The μ(eff) values at 298 K of 1-4 correspond to S = 3/2, S = 0, S = 1 and S = 1/2, respectively. Absorption spectra for all the complexes have been investigated. EPR spectral properties of the copper(II) complex 4 have been investigated, simulated and analyzed. Cyclic voltammetric experiments in CH(2)Cl(2) reveal quasireversible Co(III)-Co(II), Ni(III)-Ni(II) and Cu(II)-Cu(I) redox processes. In going from ether O to thioether S coordination, the effect of the metal coordination environment on the redox potential values of Co(III)-Co(II) (here the effect of spin-state as well), Ni(III)-Ni(II) and Cu(II)-Cu(I) processes have been systematically analyzed.
    Full-text · Article · Sep 2011 · Dalton Transactions
  • Himanshu Arora · Joan Cano · Francesc Lloret · Rabindranath Mukherjee
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    ABSTRACT: Using a (2-pyridyl)ethylamine-appended carboxylate ligand a new cluster [Cu(II)(7)(L)(4)(μ(3)-OH)(2)(H(2)O)(2)(DMF)(2)][ClO(4)](4)·4H(2)O (1) [L(2-): N-{CH(2)CH(2)(2-pyridyl)}(CH(2)CH(2)CO(2))(2)] is synthesized, as a result of 'coordination-driven self-assembly'. The structure of 1 is unique and consists of a centrosymmetric carboxylato- and hydroxo-bridged heptanuclear copper(II) cation, with body-centred anti-prismatic topology. The four crystallographically independent copper(II) centres differ markedly in their coordination geometry. In addition to establishing cluster authenticity, the structural analysis of 1 discloses two notable features. The existence of {Cu(II)(3)(μ(3)-OH)}(5+) core and H-bonded metal-coordinated carboxylate and water unit, with water acting as a proton donor. Both of these features have biological implications. Magnetic measurements reveal that in this unprecedented cluster the net magnetic-exchange is antiferromagnetic. The different types of magnetic-exchange coupling constants (J values) considered for magnetic data analysis appear to adopt a variety of values depending on the specific geometric parameters associated with two interacting copper(II) centres. Notably, for 1 a good agreement between the J values obtained from DFT calculations at the B3LYP level of theory and from the experimental data is achieved.
    No preview · Article · Sep 2011 · Dalton Transactions
  • S. Javed · V. Balamurugan · W. Jacob · A.K. Sharma · R. Mukherjee
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    ABSTRACT: Using a class of pyridyl-pyrazole ligands with variable denticity and flexibility, i. e., 1-benzyl-[3-(2′-pyridyl)]pyrazole (L10), 2-[3-(2′-pyridyl)pyrazol-1-ylmethyl]pyridine (L5) and 2,6-bis(pyrazol-1-ylmethyl)pyridine (L6), three new mercury(II) complexes - two discrete [(L10)HgII(μ-Cl)Cl]2 (1) and [(L5)HgIICl2] (2) and a coordination polymeric [(L 6)HgIICl2]·HgCl2 (3), have been synthesized and structurally characterized. In complex (1) one of the chlorides from each [(L10)HgIICl2] unit acts as a bridge, affording a dichloro-bridged mercury(II) complex with slightly distorted square-pyramidal HgN2Cl3 coordination sphere. The structure of complex (2) reveals an almost ideal square-pyramidal HgN3Cl2 coordination sphere. Complex (3) has N3Cl2 distorted square-pyramidal coordination around HgII ion with coordination by L6 (facial mode) and two Cl- ions. Notably, in complex (3) one HgCl2 molecule is present with each [(L6)HgIICl 2] unit. Due to weak interaction by HgII-coordinated Cl- ion of "[(L6)HgIICl2]" unit to HgCl2, complex (3) is a coordination polymer. Analysis of crystal packing diagram of complexes (1)-(3) reveals occurrence of a variety of non-covalent (π-π, C-H⋯π and C-H⋯Cl) interactions, which play significant role in generating supramolecular architectures of varied topology.
    No preview · Article · Sep 2011
  • Anuj Kumar Sharma · Anindita De · V. Balamurugan · Rabindranath Mukherjee
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    ABSTRACT: Using a non-planar tridentate ligand 2,6-bis(pyrazol-1-ylmethyl)pyridine (L5) two new coordination complexes [(L5)CoII(H2O)3]Cl2 (1) and [(L5)NiII(H2O)2Cl]Cl·H2O (2) have been synthesized and structurally characterized. Complex 1 has N3O3 distorted octahedral environment around CoII with coordination by L5 (two pyrazole and a pyridine nitrogen in a facial mode) and three water molecules. Complex 2 has N3O2Cl distorted octahedral geometry around NiII with meridional L5 coordination, two water molecules, and a Cl− ion. Analysis of the crystal packing diagram reveals the involvement of solvent (water as metal-coordinated and as solvent of crystallization) and counteranion (Cl−) to play significant roles in generating 1D chains, involving O–H···Cl, and O–H···O interactions.
    No preview · Article · Jun 2011 · Additives for Polymers
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    Atasi Mukherjee · Rabindranath Mukherjee
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    ABSTRACT: Using a new N,O,S-potentially tridentate ligand (H2L), a mononuclear NiII complex of composition II [Ni (L-? )2 ], (1) has been synthesized. The structure of the complex has been elucidated in the solution state using 1H NMR spectroscopy and in the solid state by X-ray crystallography. X-ray studies reveal that the NiII is surrounded by two o-iminobenzosemiquinonate(1-) p-radical ligands, providing a NiIIN2O2 square planar coordination environment. Notably, the thioether unit in each ligand remains non-coordinated. Cyclic voltammetric measurements of (1) show two one-electron reductive and two one-electron oxidative redox responses, which are ligand-centred in origin. Characterization of electrochemically-generated reduced and oxidized species has also been accomplished.
    Preview · Article · Mar 2011 · Indian Journal of Chemistry Section a
  • Himanshu Arora · Rabindranath Mukherjee
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    ABSTRACT: It is the intention of this Perspective to review the literature involving the synthesis of coordination polymers of varying dimensionality utilizing a class of chelating ligands comprising of (2-pyridyl)alkylamine-appended carboxylates performed in our group and by others. From the standpoint of functional aspects, we will focus on the magnetic properties of the chosen systems. In essence, we will provide a snapshot of this research field. © 2010 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
    No preview · Article · Nov 2010 · New Journal of Chemistry
  • Anuj Kumar Sharma · Saikat Biswas · Suman Kumar Barman · Rabindranath Mukherjee
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    ABSTRACT: A new potentially tridentate ligand HL11 consisting of 2-pyridinecarboxamide unit and azo functionality has been used, in its deprotonated form, to prepare a nickel(II) complex which has been structurally characterized. The ligand L11(−) affords a bis-complex [NiII(L11)2] (1). In 1, the two L11(−) ligands bind to the NiII center in a mer configuration. The relative orientations within the pairs of pyridyl-N, deprotonated amido-N, and azo-N atoms are cis, trans, and cis, respectively. The NiIIN2(pyridyl)N′2(amide)N″2(azo) coordination environment is severely distorted from ideal octahedral geometry. The Ni–Nam (am=amide) bond lengths are the shortest and the Ni–Nazo bond lengths are the longest. Complex 1 exhibits a quasireversible NiIII/NiII redox process. Moreover, the complex displays two ligand-centered (azo group) quasireversible redox processes. Spectroscopic (absorption and EPR) properties have been studied on coulometrically-generated nickel(III) species. To understand the nature of metal-ligand bonding interactions Density Functional Theory (DFT) calculations have been performed on 1 at the B3LYP level of theory. Calculations have also been done for closely related nickel(II) complexes of deprotonated pyridine amide ligands and comparative discussion has been made using observed results.
    No preview · Article · Oct 2010 · Inorganica Chimica Acta
  • Haritosh Mishra · Rabindranath Mukherjee
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    ABSTRACT: Structural analysis of a previously reported half-sandwich complex having three-legged “piano-stool” geometry [(η6-C6H6)RuII(L1)Cl][PF6] (1) (L1 = 2-(pyrazol-1-ylmethyl)pyridine) is described. Treatment of 1 with (i) Ag(CF3SO3) in CH3CN and (ii) NaN3 in CH3OH, and (iii) the reaction between [(η6-C6H6)Ru(L2)Cl]-[PF6] (2) (previously reported) and NaCN in C2H5OH led to the isolation of [(η6-C6H6)Ru(L1)(CH3CN)][PF6]2 (3), [(η6-C6H6)Ru(L1)(N3)][PF6] (4), and [(η6-C6H6)Ru(L2)(CN)][PF6] (5), respectively (L2 = 2-(3,5-dimethyl-pyrazol-1-ylmethyl)pyridine). The complex [(η6-C6H6)Ru(L4)Cl][PF6] (6) with a new ligand (L4 = 2-[3-(4-fluorophenyl)pyrazol-1-ylmethyl]pyridine) has also been synthesized. The structures of 3–6 have been elucidated (1H NMR spectra; CD3CN). The molecular structures of 1, 4, and 6·C6H5CH3 have been determined. Notably, the crystal-packing in these structures is governed by C–H⋯X (X = Cl, N) interactions, generating helical architectures.
    No preview · Article · Jun 2010 · Journal of Organometallic Chemistry
  • Atasi Mukherjee · Francesc Lloret · Rabindranath Mukherjee
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    ABSTRACT: Three new tripodal ligands with an N2O2 donor set, namely2-tert-butyl-6-({(2-hydroxybenzyl)[2-(2-pyridyl)ethyl]amino}methyl)-4-methylphenol (H2L1), 2-tert-butyl-6-({(2-hydroxybenzyl)[2-(2-pyridyl)ethyl]amino}methyl)-4-methoxyphenol (H2L2) and 2-tert-butyl-6-({[2-(dimethylamino)ethyl](2-hydroxybenzyl)amino}methyl)-4-methoxyphenol (H2L3) have been synthesised. Treatment of the ligands with Co(CH3CO2)2·4H2O or [Zn(H2O)6][ClO4]2 in the presence of Et3N provides the corresponding CoII and ZnII complexes of composition [MII2(L1)2] [M = Co (1) (single-crystals are a solvate with the composition [CoII2(L1)2]·2CHCl3, i.e. 1·2CHCl3); M = Zn (2)], [MII2(L2)2] [M = Co (3); Zn (4)] and [CoII2(L3)2] (5). Crystallographic analyses reveal that the complexes have closely similar diphenoxido-bridged structures. Each metal centre assumes MIIN2O3 coordination. The geometry around each metal ion in 1·2CHCl3 (τ = 0.76), 2 (τ = 0.77), 3 (τ = 0.74), 4 (τ = 0.76) and 5 [one CoII (τ = 0.49) and the other CoII (τ = 0.63)] is intermediate between ideal square-pyramidal (τ = 0) and trigonal-bipyramidal (τ = 1). Temperature-dependent magnetic studies reveal weak intramolecular antiferromagnetic exchange couplings for all the three CoII complexes(–J = 1.84, 1.32 and 5.70 cm–1 for 1, 3 and 5, respectively). Spectroscopic properties of the complexes have also been investigated. Cyclic voltammetric (CV) measurements of 1 and 2 show an irreversible oxidative response at Epa (anodic peak potential) in the range 0.60–0.75 V relative to the SCE (saturated calomel electrode), whereas two successive quasi-reversible oxidative responses can be observed for 3–5 at E1/2 values in the range 0.40–0.53 V relative to the SCE. Oxidative responses are due to the formation of MII-coordinated phenoxyl radical species. The metal-coordinated phenoxyl radical species, generated by two-electron coulometric oxidation of 3–5, were characterised by CV and by adsorption and EPR spectroscopy. The stability of such species was determined by measuring the decay constant (absorption spectroscopy), which reveals that the phenoxyl radical species of 5 is more stable than that of 3 and 4. EPR spectroscopic studies (120 K) of coulometrically generated two-electron oxidised species of 4 in CH2Cl2 (containing 0.1 M TBAP) at 298 K reveal a combination of an isotropic S = signal at g = 2 [(phenolato)(phenoxyl radical)-coordinated dizinc(II) complex] and a spin-triplet resonance (S = 1) that gives rise to the symmetric split-line pattern [bis(phenoxyl radical)-cordinated dizinc(II) complex]. To pinpoint the site of oxidation (metal- or ligand-centred) in each case, DFT calculations were performed at the B3LYP level of theory.
    No preview · Article · Jan 2010 · Berichte der deutschen chemischen Gesellschaft
  • Himanshu Arora · Francesc Lloret · Rabindranath Mukherjee
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    ABSTRACT: The synthesis of four discrete tetranuclear complexes {[Ni(II)(L(2))][ClO(4)]}(4).MeCN (1), {[Cu(II)(L(1))(O(3)SCF(3))]}(4).H(2)O (), {[Cu(II)(L(3))(OClO(3))]}(4).MeCN () and {[Cu(II)(L(4))][ClO(4)]}(4).3MeCN.4H(2)O (4), supported by a closely similar group of carboxylate-appended (2-pyridyl)alkylamine ligands [L(1)(-): 3-[N-methyl-{2-(pyridin-2-yl)ethyl}amino]propionate; L(2)(-): 3-[(2-(pyridin-2-yl)ethyl){2-(pyridin-2-yl)methyl}amino]propionate; L(3)(-): 3-[N-isopropyl-{2-(pyridin-2-yl)methyl}amino]propionate and L(4)(2-): 3-[N-{2-(pyridin-2-yl)methyl}amino]-bis(propionate)] is described. Structural characterization reveals that each Ni(II) centre in 1 has square-pyramidal Ni(II)N(3)O(2) coordination and each Cu(II) centre in 2-4 has distorted square-pyramidal Cu(II)N(2)O(3) coordination, utilizing three N and one carboxylate O in 1 and two N and carboxylate O (one in 2 and 3; two in 4) of the ligand and the fifth/fourth coordination is provided by an oxygen atom belonging to the carboxylate group of an adjacent molecule. A CF(3)SO(3)(-) or a ClO(4)(-) ion provides an O coordination in 2 and 3, respectively. Temperature-dependent magnetic studies reveal the existence of ferromagnetic exchange interaction in each case, due to the presence of equatorial-equatorial syn-anti carboxylate bridge between M(II) centres.
    No preview · Article · Nov 2009 · Dalton Transactions
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    ABSTRACT: An iron(II) complex [Fe(L5)2][ClO4]2 of a new nonplanar tridentate ligand [L5 = 2-[3-(2'-pyridyl)pyrazol-1-ylmethyl](1-methylimidazole)] has been synthesized and its spin-transition properties have been investigated. X-ray structural analysis of the solvated compound [Fe(L5)2][ClO4]2.CH3CN at 100 K and at 298 K revealed a mononuclear Fe(II)N6 pseudooctahedron with the tridentate ligand in the meridional coordination mode. Magnetic susceptibility measurements revealed LS (1A1) <--> HS (5T2) transition starting above room temperature and remained incomplete even up to 350 K, however providing evidence for the hysteretic behaviour of the transition. Photo-magnetic measurements using a 532 nm laser revealed incomplete light-induced excited spin-state trapping (LIESST). Relaxation curves in the dark exhibited a stretched exponential shape, typical for broad distributions of relaxation times. The complete photo-magnetic data were modelled using a non-cooperative master equation including a tunnelling process with distributed parameters and accounting for the bulk absorption of light. We also measured the diffuse reflectance properties, with detailed investigation of the absorption spectra and discussed the obtained features with respect to structural properties, including the suggested presence of disorder.
    No preview · Article · Sep 2009 · Dalton Transactions

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  • 1990-2015
    • Indian Institute of Technology Kanpur
      • Department of Chemistry
      Cawnpore, Uttar Pradesh, India
  • 2014
    • Indian Institute of Science Education and Research Kolkata
      Kolkata, Bengal, India
  • 2008-2013
    • Uttar Pradesh Textile Technology Institute
      Cawnpore, Uttar Pradesh, India
  • 1993-1994
    • University of Louisville
      • Department of Chemistry
      Louisville, Kentucky, United States