Issue 9, 2017

Classical hydrogen bonding and stacking of chelate rings in new copper(ii) complexes

Abstract

Three new copper(II) complexes, viz., [Cu(L)(NO3)(H2O)]H2O 1, [Cu(L)(H2O)2]NO32 and [Cu2(L)2(pyrazine)](ClO4)2·4H2O 3, were prepared using a biomimetic synthesis strategy [HL = 4-chloro-2-{(E)-[2-(pyridin-2-yl)hydrazinylidene]methyl}phenol]. Structural characterization revealed very different local geometries around copper(II) ions, being square pyramidal for mononuclear complexes (τ5 = 0.021 for 1 and τ5 = 0.13 for 2) and square planar for homobinuclear pyrazine bridged complex 3 (τ4 = 0.06). In complex 3, stacking of chelate rings was observed. This insight was thought to provide new structural evidence for the stacking of the planar chelate rings. These π-interactions provide stability to the crystal structure of homobinuclear complex 3. Magnetic measurements of bulk materials 1, 2 and 3 revealed weak antiferromagnetic coupling in all complexes. The EPR spectra of complexes 1, 2 and 3 in polycrystalline state exhibited broad signals at g ≅ 2.15 owing to spin–spin interactions between two copper ions. The cyclic voltammograms of mononuclear complexes (1 and 2) in DMSO gave one CuII/CuI irreversible wave. On the other hand, pyrazine bridged binuclear complex 3 exhibited two waves, which correspond to CuIICuII/CuIICuI and CuIICuI/CuICuI redox processes. Differential pulse voltammetry (DPV) experiments also exhibited the same reduction behavior. These complexes displayed effective antioxidant SOD activity and exhibit the outlines of a structure-based cyclic mechanism. On the basis of experimental and theoretical DFT studies, the structure–activity relationships of these complexes have also been discussed.

Graphical abstract: Classical hydrogen bonding and stacking of chelate rings in new copper(ii) complexes

Supplementary files

Article information

Article type
Paper
Submitted
09 Dec 2016
Accepted
20 Jan 2017
First published
25 Jan 2017

Dalton Trans., 2017,46, 2803-2820

Classical hydrogen bonding and stacking of chelate rings in new copper(II) complexes

Y. P. Singh, R. N. Patel, Y. Singh, D. Choquesillo-Lazarte and R. J. Butcher, Dalton Trans., 2017, 46, 2803 DOI: 10.1039/C6DT04661D

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