Kinetic measurements and quantum chemical calculations on low spin Ni(II)/(III) macrocyclic complexes in aqueous and sulphato medium

Journal of Chemical Sciences

E J Padma Malar3²  Anuradha Sankaran1 2¹  Venkatapuram Ramanujam Vijayaraghavan1¹ 

[1]Department of Physical Chemistry, University of Madras, Guindy Campus, Chennai 600 025, India$$

[2]National Centre for Ultrafast Processes, University of Madras, Taramani Campus, Chennai 600 113, India$$

关键词: Ni(III) macrocyclic complexes;    kinetics;    density functional theory;    BP86;    def2-TZVP;    hydrogen bonding;   

DOI  :  

来源: Indian Academy of Sciences

【 摘 要 】

Cu(II) ion catalyzed kinetics of oxidation of H2O2 by [NiIIIL2] (L2 = 1,8-bis(2-hydroxyethyl)-1,3,6,8,10,13-hexaazacyclotetradecane) was studied in aqueous acidic medium in the presence of sulphate ion. The rate of oxidation of H2O2 by [NiIIIL2] is faster than that by [NiIIIL1] (L1 = 1,4,8,11-tetraazacyclote-tradecane) in sulphate medium. DFT calculations at BP86/def2-TZVP level lead to different modes of bonding between [NiL]II/III and water ligands (L = L1 and L2). In aqueous medium, two water molecules interact with [NiL]II through weak hydrogen bonds with L and are tilted by ∼23° from the vertical axis forming the dihydrate [NiL]2+.2H2O. However, there is coordinate bond formation between [NiL1]III and two water molecules in aqueous medium and an aqua and a sulphato ligand in sulphate medium leading to the octahedral complexes [NiL1(H2O)2]3+ and [NiL1(SO4)(H2O)]+. In the analogous [NiL2]III, the water molecules are bound by hydrogen bonds resulting in [NiL2]3+.2H2O and [NiL2(SO4)]+.H2O. As the sulphato complex [NiL2(SO4)]+.H2O is less stable than [NiL1(SO4)(H2O)]+ in view of the weak H-bonding interactions in the former it can react faster. Thus the difference in the mode of bonding between Ni(III) and the water ligand can explain the rate of oxidation of H2O2 by [NiIIIL] complexes.

【 授权许可】

Unknown