• Ramgopal Bhattacharyya

      Articles written in Journal of Chemical Sciences

    • Reactivity of the Re-NO centre: Proton induced oxidation of Re(NO)2+ to Re(NO)3+. Synthesis and characterisation of some Re(II) thiocyanato-halogenonitrosyl complexes

      Ramgopal Bhattacharyya Anup K Dasmahapatra Partha S Roy

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      The Re(NO)2+ moiety as [Re(NO)(NCS)3H2O] or [Re(NO)(NCS)2(L-L)H2O]· [L-L = phen (1,10-phenanthroline) or bipy (2,2′-bipyridine)] undergoes proton-induced oxidation reaction with HX (X = Cl, Br) to produce a Re(NO)3+ moiety. The spectral and physico-chemical data suggest that the anionic complex is 5 coordinate and the neutral one is 6 coordinate with axial NO group and two NCS ligands intrans-equatorial positions. The complex, [Re(NO)(NCS)2(phen)Br]·H2O shows complicated magnetic behaviour which is discussed in the paper. The ESR spectrum of this compound shows typical rhenium hyperfines and <g>-tensor anisotropy compatible with the loss of axial symmetry. However, the spectrum of [Re(NO)(NCS)2Br2] quite reasonably shows axial symmetry, other features being grossly comparable to the L-L compounds. The anionic species and the neutral L-L complex show irreversible one-electron oxidation waves at different voltages. This may correspond to a conversion of Re(NO)3+ to Re(NO)4+ in both the cases. Interestingly enough, only the neutral complexes exhibit an irreversible reduction wave due probably to a conversion of Re(NO)3+ to Re(NO)2+.

    • Synthesis, characterization and reactivity of oxomolybdenum(V) complexes with ONS and NNS donors

      Samiran Bhattacharjee Ramgopal Bhattacharyya

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      The monomeric oxomolybdenum(V) complexes, [MoOLCl2]1a-1d [HL = S-benzyl/methyl 3-(2-pyridyl)methylenedithiocarbazate (1a and1b), or N-methyl-S-benzyl/methyl 3-(2-hydroxy phenyl)methylenedithiocarbazate (1c and1d) are synthesized by the reaction of MoOCl52− with HL ligands. All these complexes show magnetic moment of about 1.7 B.M. The complexes,1a and1b, exhibit rhombicg-tensor anisotropy (like xanthine oxidase) whilst1c and1d show axial spectrum. The above complexes undergo irreversible electrochemical reduction furnishing Mo(IV) species and the potentials are dependent on the S-substituents. Reactions of MoOX5 (X = Cl or Br) with H2L1 [H2L1 = S-methyl 3-(5-R-2-hydroxyphenyl)methylenedithiocarbazate] (R = H, CH3, Cl, Br) produce complexes of thiolatobridged dimers, [Mo2O2L21X2], which show sub-normal magnetic moments at room temperature. The metal-centred irreversible oxidation and reduction of these complexes show expected dependence on the R-substituents of the salicyl phenyl ring of the ligands.

    • Ligand control on the synthesis and redox aspects of mononuclear manganese-(III) and -(IV) complexes with tridentate ONS-coordination

      Rina Mukhopadhyay Samiran Bhattacharjee Ramgopal Bhattacharyya

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      MnCl2·4H2O reacts with benzohydroxamic acid (BHAH2) in aqueous/non-aqueous solution (alkaline) forming manganese(IV) complexes of the type (PPh4)2[Mn(BHA)3]·3H2O. Its IR data suggest the hydroximato mode of coordination (O, O). This complex in frozen solution exhibits axial spectra with strong zero field splitting giving rise to ag≈4 signal which is more intense than that forg≈2. The solid, however, shows rhombic spectra. A probable reason for this difference is assigned. Trifunctional (ONS) Schiff bases H2L1 and H2L2 (5-R-salicylaldehyde thiosemicarbazone and 5-R-salicyl aldehyde-4-phenyl thiosemicarbazone, respectively; R=H, Me or Br) furnish Mn(IV) complexes of the type [MnL2](L=L1 or L2), whereas H2L3 and H2L4 (H2L3=S-methyl 3-(5-R-2-hydroxyphenyl) methylene dithiocarbazate; H2L4=S-benzyl 3-(5-R-2-hydroxyphenyl) methylene dithiocarbazate; R=H, Me or Br) afford manganese(III) complexes of the type [MnL(O2CMe)] or [MnL(acac)] (acac=acetylacetonate, L=L3 or L4), when treated with MnII (O2CMe)2·4H2O or [MnIII(acac)3] in ethanol medium in air. The EPR spectra of the manganese(IV) complexes in frozen dimethyl formamide (dmf)-methanol solution show weak and strong signals at 〈g〉≈4·0 and ≈2·0 respectively, implying a small zero field splitting. The 〈g〉≈2·0 shows hyperfine (55Mn) as well as forbidden lines. Cyclic voltammograms of these complexes scanned in DMF show reversible and quasi-reversible MnIV-MnIII couple, theE2980 values of which are significantly affected by the electronic effects of the R-substituents in the salicyl phenyl ring and those attached to the carbon atom bound to the thiolate functionality of the ligands. The HammettσP values of the R-substituents are linearly correlated with theE2980 values.

    • Oxygen-rich molybdenum and chromium complexes: Synthesis, structure and catalysis

      Ratna Bandyopadhyay Sudeb Biswas Ramgopal Bhattacharyya

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