Rabindranath Mukherjee

Indian Institute of Science Education and Research Kolkata, Kolkata, Bengal, India

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Publications (102)272.34 Total impact

  • 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.
    Proceedings of the National Academy of Sciences, India - Section A 06/2014; 84(2). · 0.17 Impact Factor
  • 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.
    Zeitschrift für anorganische Chemie 03/2014; · 1.16 Impact Factor
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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.
    Inorganic Chemistry 01/2014; 53(1):36-48. · 4.59 Impact Factor
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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.
    Journal of inorganic biochemistry 08/2013; · 3.25 Impact Factor
  • 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.
    Inorganic Chemistry 04/2013; · 4.59 Impact Factor
  • 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.
    Coordination Chemistry Reviews 01/2013; 257(2):350–368. · 11.02 Impact Factor
  • 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).
    Inorganic Chemistry 11/2012; · 4.59 Impact Factor
  • Himanshu Arora, Suman K Barman, Francesc Lloret, Rabindranath Mukherjee
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    ABSTRACT: Using the dinucleating phenol-based ligand 2,6-bis[3-(pyridin-2-yl)pyrazol-1-ylmethyl]-4-methylphenol] (HL(2)), in its deprotonated form, the six new dinuclear complexes [M(II)(2)(L(2))(μ-O(2)CMe)(2)(MeCN)(2)][PF(6)] (M = Mn (2a), Co (3a), Zn (4a)) and [M(II)(2)(L(2))(μ-O(2)CMe)(2)(MeCN)(2)][BPh(4)] (M = Mn (2b), Co (3b), Zn (4b)) have been synthesized. Crystallographic analyses on 2b·2MeCN, 3b·2MeCN, and 4b·2MeCN reveal that these complexes have closely similar μ-phenoxo bis(μ-carboxylato) structures. The physicochemical properties (absorption and ESI-MS spectral data, 2a,b, 3a,b, and 4a,b; (1)H NMR, 4a,b) of the cations of 2a-4a are identical with those of 2b-4b. Each metal ion is terminally coordinated by a pyrazole nitrogen and a pyridyl nitrogen from a 3-(pyridin-2-yl)pyrazole unit and a solvent molecule (MeCN). Thus, each metal center assumes distorted-octahedral M(II)N(3)O(3) coordination. Temperature-dependent magnetic studies on Mn(II) and Co(II) dimers reveal the presence of intramolecular antiferromagnetic (J = -8.5 cm(-1)) for 2b and ferromagnetic exchange coupling (J = +2.51 cm(-1)) for 3b, on the basis of the Hamiltonian H = -JS(1)·S(2). The exchange mechanism is discussed on the basis of magneto-structural parameters (M···M distance). Spectroscopic properties of the complexes have also been investigated. The pH titration and kinetics of phosphatase (transesterification) activity on 2-hydroxypropyl-p-nirophenylphosphate (HPNP) were studied in MeOH/H(2)O (33%, v/v) with 2a-4a, due to solubility reasons. This comparative kinetic study revealed the effect of the metal ion on the rate of hydrolysis of HPNP, which has been compared with what we recently reported for [Ni(II)(2)(L(2))(μ-O(2)CMe)(2)(MeOH)(H(2)O)][ClO(4)] (1a). The efficacy in the order of conversion of substrate to product (p-nitrophenolate ion) follows the order 4a > 3a > 2a > 1a, under identical experimental conditions. Notably, this trend follows the decrease of pK(a) values of M(II)-coordinated water (7.95 ± 0.04 and 8.78 ± 0.03 for 1a, 7.67 ± 0.08 and 8.69 ± 0.06 for 2a, 7.09 ± 0.05 and 8.05 ± 0.06 for 3a, and 6.20 ± 0.04 and 6.80 ± 0.03 for 4a). In this work we demonstrate that the stronger the Lewis acidity (Z(eff)/r) of the metal ion, the more acidic is the M(II)-coordinated water and the greater is the propensity of the metal ion to catalyze hydrolysis of the activated phosphate ester HPNP. Notably, the observed k(2) values (M(-1) s(-1)) for Mn(II) (2a, 0.152), Co(II) (3a, 0.208), and Zn(II) (4a, 0.230) complexes (1a, 0.058; already reported) linearly correlate with Z(eff)/r values of the metal ion. In each case a pseudo-first-order kinetic treatment has been done. Kinetic data analysis of complexes 2a-4a were also done following Michaelis-Menten treatment (catalytic efficiency k(cat)/K(M) values 0.170 M(-1) s(-1) for 2a, 0.194 M(-1) s(-1) for 3a and 0.161 M(-1) s(-1) for 4a; for 1a the value is 0.089 M(-1) s(-1)). Temperature-dependent measurements were done to evaluate kinetic/thermodynamic parameters for the hydrolysis/transesterification of HPNP and yielded comparable activation parameters (E(a) (kJ mol(-1)): 71.00 ± 4.60 (1a; reported), 67.95 ± 5.71 (2a), 62.60 ± 4.46 (3a), 67.80 ± 3.25 (4a)) and enthalpy/entropy of activation values (ΔH(‡) (kJ mol(-1)) = 68.00 ± 4.65 (1a; reported), 65.40 ± 5.72 (2a), 60.00 ± 4.47 (3a), 65.29 ± 3.26 (4a); ΔS(‡) (J mol(-1) K(-1)) = -109.00 ± 13 (1a; reported), -107.30 ± 16 (2a), -122.54 ± 14 (3a), -104.67 ± 10 (4a)). The E(a) values for all the complexes are comparable, suggesting a closely similar reaction barrier, meaning thereby similar course of reaction. The ΔS(‡) values are consistent with an associative process. Positive ΔH(‡) values correspond to bond breaking of the activated complex as a result of nucleophilic attack at the phosphorus atom, releasing cyclic phosphate and p-nitrophenolate ion. These data have helped us to propose a common mechanistic pathway: deprotonation of a metal-bound species to form the effective nucleophile, binding of the substrate to the metal center(s), intramolecular nucleophilic attack on the electrophilic phosphorus atom with the release of the leaving group, and possibly regeneration of the catalyst.
    Inorganic Chemistry 04/2012; 51(10):5539-53. · 4.59 Impact Factor
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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.
    Dalton Transactions 09/2011; 40(40):10758-68. · 4.10 Impact Factor
  • 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.
    Dalton Transactions 09/2011; 40(39):10055-62. · 4.10 Impact Factor
  • 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.
    Additives for Polymers 06/2011; 372(1):327–332.
  • 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.
    New Journal of Chemistry 11/2010; 34(11):2357-2365. · 3.16 Impact Factor
  • 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.
    Journal of Organometallic Chemistry 06/2010; 695(14):1753-1760. · 2.00 Impact Factor
  • 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.
    Berichte der deutschen chemischen Gesellschaft 01/2010; 2010(7):1032 - 1042. · 2.94 Impact Factor
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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.
    Inorganica Chimica Acta - INORG CHIM ACTA. 01/2010; 363(12):2720-2727.
  • 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.
    Dalton Transactions 11/2009; · 4.10 Impact Factor
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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.
    Dalton Transactions 09/2009; · 4.10 Impact Factor
  • Sukanta Mandal, V Balamurugan, Francesc Lloret, Rabindranath Mukherjee
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    ABSTRACT: Four dinuclear nickel(II) complexes [Ni(II)(2)(L(1))(O(2)CMe)(2)(H(2)O)(2)][PF(6)].MeOH.3H(2)O (1), [Ni(II)(2)(L(1))(O(2)CMe)(2)(NCS)] (2), [Ni(II)(2)(L(2))(O(2)CMe)(2)(MeOH)(H(2)O)][ClO(4)] (3), and [Ni(II)(2)(L(2))(O(2)CMe)(2)(MeOH)(H(2)O)][BPh(4)].3MeOH.H(2)O (4) have been synthesized [HL(1): 2,6-bis[N-methyl-N-(2-pyridylethyl)amino]-4-methylphenol; HL(2): 2,6-bis[3-(pyridin-2-yl)pyrazol-1-ylmethyl]-4-methylphenol]. Complexes 1, 3, and 4 are new while complex 2 was reported previously by Fenton and co-workers (the structure of 2 was presented but no physicochemical properties of this complex were reported; in this work such studies have been completed). X-ray crystallographic analyses of 1 and 4 reveal that each nickel(II) center is six-coordinate, terminally coordinated by two nitrogen donors [(pyridin-2-yl)ethylamine unit in 1 and 3-(pyridin-2-yl)pyrazole moiety in 4], and bridged by an endogenous phenolate ion. Each of the acetate ions in 1 adopts a eta(2)-coordination mode (chelating) whereas in 4 each is coordinated in a mu-eta(1):eta(1) syn-syn bridging mode. In 1 each Ni(II) center has water coordination whereas in 4 one Ni(II) center has a methanol and the other has water coordination. The X-ray structure of 3 could not be determined. The physicochemical properties (electronic spectroscopy and cyclic voltammetry) of the cation of 3 are identical to that of 4. Magnetic susceptibility measurements have revealed the occurrence of ferromagnetic coupling of spins of the nickel(II) centers in 2 [J = +9.80 cm(-1)]. The nickel(II) centers in 1 and 3 are antiferromagnetically coupled, but to different extents [J = -48.4 cm(-1) (1); J = -1.24 cm(-1) (3)]. The magnetic properties are correlated with the nature of bridges between the nickel(II) ions. The two coordinated aqua ligands in 1 and the aqua and methanol ligands in 3 have enabled these dinuclear nickel(II) complexes to function as catalysts in the hydrolysis of 2-hydroxypropyl-p-nitrophenylphosphate (HPNP). Complex 1 is more effective in the conversion of substrate to product (p-nitrophenolate ion) than 3, under identical experimental conditions. Pseudo first-order kinetic treatment has been done for complexes 1 and 3. Temperature-dependent measurements were done to evaluate kinetic/thermodynamic parameters for the hydrolysis/transesterification reaction of HPNP and to propose a mechanistic pathway. The activation parameters are DeltaH(++) = 64 kJ mol(-1), DeltaS(++) = -104 J mol(-1) K(-1) for 1 and DeltaH(++) = 68 kJ mol(-1), DeltaS(++) = -109 J mol(-1) K(-1) for 3. A mechanism consistent with the kinetic data is presented.
    Inorganic Chemistry 08/2009; 48(16):7544-56. · 4.59 Impact Factor
  • Himanshu Arora, Francesc Lloret, Rabindranath Mukherjee
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    ABSTRACT: Four new complexes [MnII(L1OO)(H2O)][ClO4]·2H2O (1), [ZnII(L1OO)][ClO4]·2H2O (2), [CuII(L3OO)][CF3SO3]·H2O (3), and [ZnII(L3OO)][ClO4] (4) (L1OO– = 3-[(2-(pyridine-2-yl)ethyl){2-(pyridine-2-yl)methyl}amino]propionate; L3OO– = 3-[(2-(pyridine-2-yl)ethyl){(dimethylamino)ethyl}amino]propionate) have been synthesized and characterized by elemental analysis, IR, and UV/Vis spectroscopy. Structural analysis revealed that 1, 3, and 4 are one-dimensional chain-like coordination polymers. In 1 distorted octahedral MnN3O3 and in 3 square-pyramidal CuN3O2 coordination is satisfied by three nitrogen atoms and an appended carboxylate oxygen atom of the ligand, and an oxygen atom belonging to the carboxylate group of an adjacent molecule. In 4 trigonal bipyramidal ZnN3O2 coordination environment is provided by two nitrogen atoms and an appended carboxylate oxygen atom of the ligand in the equatorial plane, and the two axial positions are satisfied by a tertiary amine nitrogen and an oxygen atom belonging to the carboxylate group of an adjacent molecule. In 1 the MnII center is coordinated by an additional water molecule. In these complexes each monomeric unit is sequentially connected by syn-anti carboxylate bridges. Temperature-dependent magnetic susceptibilities for 1 and 3 are measured, revealing antiferromagnetic interactions through syn-anti carboxylate bridges between the MII centers. Analysis of the crystal packing diagram reveals that in 1 extensive π–π stacking involving alternate pyridine rings of adjacent 1D chain exists, which eventually lead to the formation of a 2D network structure. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
    Berichte der deutschen chemischen Gesellschaft 06/2009; 2009(22):3317 - 3325. · 2.94 Impact Factor
  • Vibha Mishra, Haritosh Mishra, Rabindranath Mukherjee
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    ABSTRACT: Mononuclear CoII and NiII complexes [(L1)CoII(H2O)2][ClO4]2 (1) and [(L1)NiII(MeCN)2][BPh4]2 (3) (L1 = 2,2′-[propane-1,3-diylbis(1H-pyrazole-1,3-diyl)]dipyridine) display a quasireversible MII/MI redox process (E1/2 = –0.96 V vs. SCE, ΔEp = 110 mV for 1; E1/2 = –0.71 V vs. SCE, ΔEp = 90 mV for 3). The dinuclear CoII complex [(L1)2CoII2(μ-O2CMe)2][BPh4]2 (2) displays a quasireversible reductive response (E1/2 = –1.46 V vs. SCE, ΔEp = 120 mV), supposedly due to CoII2/CoI2 redox process. For these complexes chemical (NaBH4) and electrochemical reduction generate CoI and NiI species. The existence of dark purple NiI species has been authenticated by its UV/Vis spectral feature (crystal-field transition at 901 nm and metal-to-ligand charge-transfer transition at 537 nm) and axial EPR spectrum (g∥ = 2.27 and g⟂ = 2.08). Dark greenish blue/bright green CoI species were characterized by absorption spectroscopy. Reaction of chemically generated CoI species with CH3I resulted in the formation of dimethyl-CoIII complexes. Notably, CoI species generated from monomeric complex 1 led to the formation of two products: a mononuclear complex [(L1)CoIII(CH3)2][ClO4] (4) (minor) and a dinuclear complex [(L1)2CoIII2(CH3)4][ClO4]2 (5) (major). In contrast, when the dimeric complex 2 was reduced with NaBH4 and reacted with CH3I the monomeric complex [(L1)CoIII(CH3)2][BPh4] (6) was isolated in reasonable yield. All three organometallic dialkyl-CoIII complexes 4–6 have been characterized by elemental analysis, 1H NMR spectroscopy, and X-ray crystallography.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
    Berichte der deutschen chemischen Gesellschaft 06/2009; 2009(20):2973 - 2980. · 2.94 Impact Factor

Publication Stats

380 Citations
272.34 Total Impact Points

Institutions

  • 2014
    • Indian Institute of Science Education and Research Kolkata
      Kolkata, Bengal, India
  • 1992–2014
    • Indian Institute of Technology Kanpur
      • Department of Chemistry
      Cawnpore, Uttar Pradesh, India
  • 2004
    • Justus-Liebig-Universität Gießen
      • Institut für Anorganische und Analytische Chemie
      Gießen, Hesse, Germany
  • 1997
    • University of Louisville
      • Department of Chemistry
      Louisville, Kentucky, United States