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

• # Fulltext

https://www.ias.ac.in/article/fulltext/jcsc/127/07/1287-1298

• # Keywords

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

• # Abstract

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 $\sim$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.

• # Author Affiliations

1. Department 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 624 622, India
3. National Centre for Ultrafast Processes, University of Madras, Taramani Campus, Chennai 600 113, India

• # Journal of Chemical Sciences

Volume 135, 2023
All articles
Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019