• R Venkatesan

      Articles written in Journal of Chemical Sciences

    • Synthesis, spectral, magnetic and electrochemical properties of new binuclear unsymmetrical aminoacid ligands and their Cu(II) complexes with bridging and non bridging motifs

      Indu Rekha Naganathan R Venkatesan P Sambasiva Rao T M Rajendiran

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      The synthesis, spectral, magnetic and electrochemical properties of a series of binuclear Cu(II) complexes of new unsymmetrical binucleating ligands (H2L1, H2L2) are described where H2L1=4-methyl-2-[N-methyl piperazin-1-yl) methyl]-6-[(prolin-1-yl)-methyl] phenol and H2L2=4-bromo-2-[N-methyl piperazin-1-yl)methyl]-6-[(prolin-1-yl)]-methyl] phenol. The exogenous ligands were incorporated into the complexes: hydroxo [Cu2 L(OH)(H2O)2] ClO4·H2O (L1=1a, L2=1b), acetato, [Cu2L(OAc)2]·H2O (L1=2a, L2=2b), nitrito, [Cu2(L(NO2)2(H2O)2] (L1=3a, L2=3b), azido, [CuL(N3)2]·3H2O (L1=4a, L2=4b). Complexes 1a, 1b and 2a, 2b contain bridging exogenous groups, while 3a, 3b and 4a, 4b possess only openμ-phenolato structures. Both, the ligands and complexes were characterised by spectral studies. The magnetic susceptibility of the complexes have been measured in the temperature range (77–300K) and the exchange coupling parameter (2J) was determined from least square fitting of the data. The strength of the antiferromagnetic interaction is in the order NO2=N3>OAc>OH. The redox behaviour of these complexes in acetonitrile reveal highly quasi reversible behaviour due to chemical or/ and stereochemical changes subsequent to electron transfer. 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.

    • Exogenous bridging and nonbridging in Cu(II) complexes of Mannich base ligands: Synthesis and physical properties

      S Sujatha T M Rajendiran R Kannappan R Venkatesan P Sambasiva Rao

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      Preparation of pentadentate ligands L1, L2, L3 and L4, where L1 = 4-chloro-3-methyl-2[(prolin-1-yl)methyl]-6-[N-phenyl piperazin-1-yl)methyl]phenol, L2 = 4-ethyl-2-[(prolin-1-yl)methyl]-6-[(N-phenyl piperazin-1-yl)methyl]phenol, L3 = 4-chloro-3-methyl-2-[(prolin-1-yl)methyl]-6-[N-methyl piperazin-1-yl]methyl phenol, L4 = 4-methoxy-2-[(prolin-1-yl)methyl]-6-[(N-phenyl piperazin-1-yl)methyl]phenol is described together with that of the corresponding Cu(II) complexes with various bridging motifs like OH, OAc and NO2. The complexes are characterized by elemental analysis, electrochemical and electron paramagnetic spectral studies. Redox properties of the complexes in acetonitrile are highly quasireversible due to the chemical or/and stereochemical changes subsequent to electron transfer. The complexes show resolved copper hyperfine EPR at room temperature, indicating the presence of weak antiferromagnetic coupling between the copper atoms. Strengths of the antiferromagnetic interactions are in the order NO2>OAc>OH.

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