Classical hydrogen bonding and stacking of chelate rings in new copper(ii) complexes.
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/CuIirreversible wave. On the other hand, pyrazine bridged binuclear complex 3 exhibited two waves, which correspond to CuIICuII/CuIICuIand CuIICuI/CuICuIredox 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.
Department of Chemistry, A. P. S. University, Rewa, M.P., 486003, India. rnp64@ymail.com.
Yogendra Pratap
http://orcid.org/0000-0002-9083-1558
YP
Singh
Department of Chemistry, A. P. S. University, Rewa, M.P., 486003, India. rnp64@ymail.com.
Ram N
http://orcid.org/0000-0001-9211-9022
RN
Patel
Department of Chemistry, A. P. S. University, Rewa, M.P., 486003, India. rnp64@ymail.com.
Yogendra
Y
Singh
Laboratorio de Estudios Cristalográficos, IACT, CSIC-Universidad de Granada, Av. de las Palmeras 4, E-18100 Armilla, Granada, Spain.
Duane
http://orcid.org/0000-0002-7077-8972
D
Choquesillo-Lazarte
Department of Inorganic & Structural Chemistry, Howard University, Washington DC, 22031 USA.
R J
RJ
Butcher