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      https://www.ias.ac.in/article/fulltext/jcsc/129/02/0193-0202

    • Keywords

       

      Nickel(III) macrocycle; hydrogen peroxide oxidation; Cu(II); H-bond; DFT calculations.

    • Abstract

       

      The Cu(II) ion-catalysed kinetics of oxidation of H ₂O ₂ by [NiIIIL] [where L = L₁ (cyclam) and L ₂ (1,8-bis(2-hydroxyethyl)-1,3,6,8,10,13-hexaazacyclotetradecane)] was studied in the pH range of 3.6–5.6 in acetic acid-acetate buffer medium at 25◦C in the presence of sulphate ion. The ionic strength (I) was maintained at 0.5 M (NaClO₄). The rate constants showed an inverse acid dependence and [NiIIIL ₂] was observed to be more stable than [NiIIIL₁]. The rate of the reaction of both complexes with hydrogen peroxide shows contrastingbehaviour at pH > 2.5 when compared to the same reaction in perchloric acid medium. DFT calculations performed on the complexes [NiIIIL₁ (SO₄)(OAc)] and [NiIIIL ₂ (SO₄)(OAc)] reveal that both the acetate and sulphate ligands are axially coordinated to the metal centre. In addition, there is strong hydrogen bonding between the axial ligand and NH hydrogen of the macrocyclic ligand. The computed covalent bond ordersin the aqueous medium predict that the acetate forms stronger coordinate bond with Ni ion than the sulphate ligand. The hydroxyl group present in one of the pendant groups of L ₂ forms a strong hydrogen bond with thesulphate ligand which leads to additional stability in [NiIIIL ₂ (SO₄)(OAc)].

    • Author Affiliations

       

      ANURADHA SANKARAN1 2 E J PADMA MALAR3 VENKATAPURAM RAMANUJAM VIJAYARAGHAVAN1

      1. aDepartment of Physical Chemistry, University of Madras, Guindy Campus, Chennai 600 025, India
      2. Department of Chemistry, PSNA College of Engineering and Technology, Kothandaraman Nagar, Dindigul, Tamilnadu 624 622, India
      3. National Centre for Ultrafast Processes, University of Madras, Taramani Campus, Chennai 600 113, India
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