• Sanjib Pal

      Articles written in Journal of Chemical Sciences

    • Osmium arylazoimidazoles: Synthesis, spectral characterisation and redox properties of the complexes

      Sanjib Pal Tarun Kumar Misra Pabitra Chattopadhyay Chittaranjan Sinha

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      Arylazoimidazoles (RaaiH,p-R-C6H4N=N-C3H3N2, R=H, Me, OMe, Cl and NO2) are N,N′-chelators. On reaction with (NH4)2[OsCl6], two classes of isomers blue-violetctc-Os(RaaiH)2Cl2 and red-violetccc-Os(RaaiH)2Cl2 have been isolated. The complexes have been characterised by elemental analyses, IR, UV-Vis and1H NMR spectral data. The N=N stretching is red shifted by 70–80 cm−1 compared to the free ligand values and indicatesd(Os)→π*(azo) charge shifting. This is supported by MLCT transition in the visible region.1H NMR spectra suggest that blue-violet isomers areC2-symmetric and red-violet isomers areC1-symmetric. Redox studies show the Os(III)/(II) couple of both isomers at 0·6–0·7 Vvs SCE and two successive azo reductions.

    • Studies on the reactivity of cis-RuCl2 fragment in Ru(PPh3)2(TaiMe)Cl2 with N,N-chelators (TaiMe = 1-methyl-2-(p-tolylazo)imidazole). Spectral and electrochemical characterisation of the products

      Sanjib Pal Chittaranjan Sinha

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      Dechlorination of Ru(PPh3)2(TaiMe)Cl2 (TaiMe = p-Me-C6H4-N=N-C3H2NN(1)-Me (1), 1-methyl-2-(p-tolylazo)imidazole) has been carried out in acetone solution by Ag+ and reacted with N,N’-chelators to synthesise [Ru(PPh3)2 (TaiMe)(N,N’)]2+. The complexes have been isolated as their perchlorate salts. The N,N’ chelators are 1-alkyl-2-(phenylazo)imidazoles (PaiX, X = Me, Et, CH2Ph); 2-(arylazo)pyridines, (Raap,p-R-C6H4-N=N-C5H4N; R = H, Me, Cl); 2-(arylazo)pyrimidines (Raapm,p-R-C6H4-N=N-C3N2H2; R = H, Me, Cl); 2,2’-bipyridine (bpy) and 1,10-phenanthroline (o-phen). Unsymmetrical N,N’ chelators may give two isomers and this is indeed observed. The1H NMR spectral data refer to the presence of two isomers in the mixture in different proportions. With consideration of coordination pairs in the order of PPh3, PPh3; N,N (N refers to N(immidazole)) and N’,N (N’ refers to N(azo)), the complexes have been characterised astrans-cis-cis andtrans-trans-trans configuration; the former predominates in the mixture. Electrochemical studies exhibit high potential Ru(III)/Ru(II) couple and quasireversible N=N reduction. Electronic spectra show high intensity (ε ∼ 104) MLCT transition in the visible region (520 ±10) nm along with a shoulder (ε ∼ 103) in the longer wavelength region.

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