Related Experiment Video
Updated: Jun 18, 2025
Thermochemical Studies of NiII and ZnII Ternary Complexes Using Ion Mobility-Mass Spectrometry
Published on: June 8, 2022
Tetranuclear NiII-Mannich base complex with oxygenase, water splitting and ferromagnetic and antiferromagnetic
Arka Patra1, Avijit Das1, Abhimanyu Sarkar1
1Department of Chemistry, Jadavpur University, Kolkata-700032, India. crsjuchem@gmail.com.
Abstract:
A new Mannich base (2-(4-(2-hydroxy-3-methoxy-5-methylbenzyl)-piperazin-1-yl)methyl)-6-methoxy-4-ethylphenol (H2L) and its tetranuclear NiII complex [Ni4L2(μ1,1-Cl)2(H2O)4]Cl2 (compound 1) are characterised using single-crystal X-ray diffraction measurements. Compound 1 contains four different NiII centres in a rhombus-like structure. Two Ni atoms (Ni1 and Ni2) have a NiN2O4 coordination sphere, while the other two (Ni3 and Ni4) have a NiO4Cl2 coordination environment and Ni-Cl-Ni bridges connect them. Ni1 and Ni2 are linked to Ni3 and Ni4 by phenoxide bridges. Variable temperature magnetic susceptibility measurements of 1 indicate the presence of alternating antiferromagnetic coupling (J1 = -6.6(1) cm-1) through the phenoxide bridge along the sides of the rhombus and ferromagnetic coupling (J2 = 8.4(1) cm-1) through the double Cl bridge along the short diagonal of the rhombus with a zero-field splitting of |D| = 2.7(1) cm-1. Compound 1 shows oxidase (catecholase-like and phenoxazinone synthase-like) activity. The oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) gives 3,5-di-tert-butylquinone (3,5-DTBQ) and H2O2 and the oxidation of o-aminophenol (OAP) produces 2-aminophenoxazin-3-one (APX) and H2O with turnover numbers of 28.32 and 17.52 h-1, respectively, under aerobic conditions. A mechanism for the oxidase activity catalysed by compound 1 is proposed in line with ESI-mass spectrometry, EPR spectroscopy, and electrochemical data. The reaction involves the cleavage of the tetranuclear Ni4-core to form a mononuclear NiII complex in the presence of the substrate (3,5-DTBC/OAP). This NiII complex is reduced to NiI with the concomitant oxidation of the substrate (3,5-DTBQ/APX). Formation of a radical intermediate is confirmed using EPR. In the catecholase-like activity, O2 is reduced to H2O2 while in the phenoxazinone synthase-like activity O2 produces H2O. Compound 1 participated in oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in a strongly basic medium with an onset potential of 418 mV and a Tafel slope of 121 mV dec-1 for OER and an onset potential of 477 mV and Tafel slope of 146 mV dec-1 for HER.
More Related Videos
![Protein Film Infrared Electrochemistry Demonstrated for Study of H2 Oxidation by a [NiFe] Hydrogenase](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F55858.jpg&w=3840&q=50)
Related Concept Videos
03:02Colors and Magnetism
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human...
02:42Valence Bond Theory
02:46Crystal Field Theory - Tetrahedral and Square Planar Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
02:51Metal-Ligand Bonds
In these complexes, transition metals form coordinate covalent bonds, a kind of Lewis acid-base interaction in which both of the electrons in the bond are contributed by a donor (Lewis base) to an electron acceptor (Lewis acid). The Lewis acid in...
02:58Crystal Field Theory - Octahedral Complexes
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...