Unprecedented tetranuclear complexes with "weighing balance shaped" topology: single crystal structures, unusual EPR spectra, magnetic properties and antioxidant activity

Dalton Trans. 2017 Sep 12;46(35):11860-11874. doi: 10.1039/c7dt02595e.

Abstract

Using the 2-hydroxy-N'-[(E)-phenyl(pyridin-2-yl)methylidene]benzohydrazide ligand and dicarboxylate anions (succinate and malonate), two new copper(ii) complexes of formula [Cu4(μ-L)4(μ-CH2(COO)2)(H2O)3](NO3)2·4H2O (1) and [Cu4(μ-L)4(μ-CH2-CH2(COO)2)(H2O)](NO3)2] (2) have been synthesized and characterized by single crystal X-ray diffraction. Complexes 1 and 2 contain a dicarboxylate bridged tetranuclear Cu(ii) cationic unit with "weighing balance shaped" topology. These compounds have also been studied by variable temperature magnetic susceptibility measurements, X-band EPR spectroscopy and electrochemistry. The unprecedented tetranuclear copper complexes 1 and 2 exhibit antiferromagnetic interactions between adjacent copper(ii) centers with magnetic exchange coupling constants (J) of J1 = -6.8 cm-1, J2 = -20.6 cm-1 and g = 2.03 for 1 and J1 = -3.1 cm-1, J2 = -13.9 cm-1 and g = 2.02 for 2. The goal for our research work is to understand the factors that govern the stability of the Cu-O(-O-C-O-) bond towards reactive oxygen species (ROS) in Cu-containing mimics utilizing a systematic approach. The antioxidant superoxide dismutase measurements indicate that these complexes behave as superoxide dismutase mimics.

MeSH terms

  • Antioxidants / chemistry*
  • Carboxylic Acids / chemistry
  • Catalysis
  • Coordination Complexes / chemical synthesis
  • Coordination Complexes / chemistry*
  • Copper / chemistry*
  • Crystallography, X-Ray
  • Electrochemical Techniques
  • Electron Spin Resonance Spectroscopy
  • Hydrogen Bonding
  • Kinetics
  • Magnetics
  • Molecular Conformation
  • Reactive Oxygen Species / chemistry

Substances

  • Antioxidants
  • Carboxylic Acids
  • Coordination Complexes
  • Reactive Oxygen Species
  • Copper