Study of behaviour of Ni(III) macrocyclic complexes in acidic aqueous medium through kinetic measurement involving hydrogen peroxide oxidation and DFT calculations

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• 作者：ANURADHA SANKARAN ; E J PADMA MALAR…
• 关键词：Nickel(III) macrocycle ; hydrogen peroxide oxidation ; Cu(II) ; H ; bond ; DFT calculations.
• 刊名：Journal of Chemical Sciences
• 出版年：2017
• 出版时间：February 2017
• 年：2017
• 卷：129
• 期：2
• 页码：193-202
• 全文大小：
• 刊物类别：Chemistry and Materials Science
• 刊物主题：Chemistry/Food Science, general;
• 出版者：Springer India
• ISSN：0973-7103
• 卷排序：129

文摘

The Cu(II) ion-catalysed kinetics of oxidation of H₂O₂ by [Ni IIIL] [where L = L₁ (cyclam) and L₂ (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 [Ni IIIL₂] was observed to be more stable than [Ni IIIL₁]. The rate of the reaction of both complexes with hydrogen peroxide shows contrasting behaviour at pH > 2.5 when compared to the same reaction in perchloric acid medium. DFT calculations performed on the complexes [Ni IIIL₁(SO₄)(OAc)] and [Ni IIIL₂(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 orders in 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 L₂ forms a strong hydrogen bond with the sulphate ligand which leads to additional stability in [Ni IIIL₂(SO₄)(OAc)].