Classical hydrogen bonding and stacking of chelate rings in new copper(ii) complexes. Issue 9 (8th February 2017)

• Record Type: Journal Article
• Authors: Singh, Yogendra Pratap; Patel, Ram N.; Singh, Yogendra; Choquesillo-Lazarte, Duane; Butcher, R. J.
• Is Part Of: Dalton transactions. Volume 46:Issue 9(2017)
• Page Start: 2803
• Page End: 2820
• Publication Date: 2017-02-08
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/c6dt04661d
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : Three new copper(ii ) complexes, viz ., [Cu(L)(NO3 )(H2 O)]H2 O1, [Cu(L)(H2 O)2 ]NO3 2 and [Cu2 (L)2 (pyrazine)](ClO4 )2 ·4H2 O3, were prepared using a biomimetic synthesis strategy [HL = 4-chloro-2-{( E )-[2-(pyridin-2-yl)hydrazinylidene]methyl}phenol]. In complex3, stacking of chelates rings was observed. Abstract : Three new copper(ii ) complexes, viz ., [Cu(L)(NO3 )(H2 O)]H2 O1, [Cu(L)(H2 O)2 ]NO3 2 and [Cu2 (L)2 (pyrazine)](ClO4 )2 ·4H2 O3, 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 ( τ 5 = 0.021 for1 and τ 5 = 0.13 for2 ) and square planar for homobinuclear pyrazine bridged complex3 ( τ 4 = 0.06). In complex3, 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 complex3 . Magnetic measurements of bulk materials1, 2 and3 revealed weak antiferromagnetic coupling in all complexes. The EPR spectra of complexes1, 2 and3 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 and2 ) in DMSO gave one Cu II /Cu I irreversible wave. On the other hand, pyrazine bridged binuclear complex3 exhibited two waves, which correspond to Cu II Cu II /Cu II Cu I and Cu II Cu I /Cu I Cu I 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.