• R Kannappan

      Articles written in Journal of Chemical Sciences

    • Synthesis, electrochemical and magnetic properties of new acylic ‘end-off’ binuclear copper(II) complexes

      T M Rajendiran R Kannappan R Venkatesan P Sambasiva Rao

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    • Synthesis and physiochemical studies on binuclear Cu(II) complexes derived from 2,6-[(N-phenylpiperazin-1-yl)methyl]-4-substituted phenols

      S Karthikeyan T M Rajendiran R Kannappan R Mahalakshmy R Venkatesan P Sambasiva Rao

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      Preparation of the ligands HL1 = 2,6-[(N-phenylpiperazin-1-yl)methyl]-p-ethylphenol; HL2 = 2,6-[(N-phenylpiperazin-1-yl)methyl]-p-methoxyphenol and HL3 = 2,6-[(N-phenylpiperazin-1-yl)methyl]-p-nitrophenol are described together with their Cu(II) complexes with different bridging units. The exogenous bridges incorporated into the complexes are: hydroxo [Cu2L(OH)(H2O)2](ClO4)2.H2O (L1=1a, L2 =1b, L3 =1c), acetato [Cu2L(OAc)2]ClO4.H2O (L1 =2a, L2 =2b, L3 =2c) and nitrito [Cu2L1(NO2)2(H2O)2]ClO4.H2O (L1=3a, L2 =3b, L3 =3c). Complexes1a,1b,1c and2a,2b,2c contain bridging exogenous groups, while3a,3b,3c possess only open μ-phenolate structures. Both the ligands and complexes were characterized by spectral studies. Cyclic voltammetric investigation of these complexes revealed that the reaction process involves two successive quasireversible one-electron steps at different potentials. The first reduction potential is sensitive to electronic effects of the substituents at the aromatic ring of the ligand system, shifting to positive potentials when the substituents are replaced by more electrophilic groups. EPR studies indicate very weak interaction between the two copper atoms. Various covalency parameters have been calculated.

    • Magnetic, catalytic, EPR and electrochemical studies on binuclear copper(II) complexes derived from 3,4-disubstituted phenol

      R Kannappan R Mahalakshmy T M Rajendiran R Venkatesan P Sambasiva Rao

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      New symmetrical compartmental binucleating ligands 2,6-bis[N-(2-dimethylaminoethyl)-N-methyl)aminomethyl]-3,4-dimethylphenol [HL1] and 2,6-bis[N-(2-diethylaminoethyl)-N-ethyl)aminomethyl]-3,4-dimethylphenol [HL2], and their copper(II) complexes [Cu2L1–2(X)]ClO4, (X = NO2-, OAc- and OH-) have been prepared. Spectral, catalytic, magnetic, EPR and electrochemical studies have been carried out. A catecholase activity study indicates that only HL1 complexes have efficient catalytic activity due to a less sterically hindered methyl group and enhanced planarity (larger-2J values) with respect to the oxidation of 3,5-di-t-butylcatechol to the corresponding quinone. Variable temperature magnetic susceptibility studies of the complexes show antiferromagnetic interaction between the copper atoms. X-band EPR signals could not be observed for polycrystalline samples both at room temperatures and liquid nitrogen, consistent with two antiferrromagnetically coupled copper centres in the solid state. EPR spectral studies in methanol solvent show well-defined four hyperfine signals at room temperature due to decomposition of the dimer into monomers. This however is not seen in frozen methanol glass, may be owing to restructuring of the monomers into dimers due to an increase in viscosity of the solvent. Electrochemical studies revealed chemically irreversible behaviour due to chemical or/and stereochemical changes subsequent to electron transfer.

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