The role of methyl and benzyl substituted dithiocarbazate of 2-acetyl pyridine for the formation of bridged dimeric and unbridged monomeric copper(II) complexes and catecholase mimetic activity of the complexes

Abstract

Monomeric [Cu(L1)Cl] (1) and dimeric [Cu(L2)Cl]2 (2) copper(II) complexes, where HL1 = methyl-2-(1-(pyridine-2-yl)ethylidene)-hydrazine-1-carbodithioate and HL2 = benzyl-2-(1-(pyridine-2-yl)ethylidene)hydrazine-1-carbodithioate, have been synthesized and characterized by X-ray crystallography, TGA and spectral methods. Complex 1 crystallizes in a space group P21/n and adopts a square planar environment surrounding the Cu ion, and complex 2 is a triclinic crystal system with space group Pī. Complex 2 is a centrosymmetric dimer where each copper atom forms two chloro bridges and completes five coordination with the tridentate NNS donor. Density functional calculations demonstrate that chloro-unbridged structure of 1 is favored by London dispersion between its layers. It is noticed that the layers are usually packed closely in the solid phase, such attractive interactions are sterically hindered between the layers of 2. Due to the presence of large phenyl group that extend from one layer to the other, the layers cannot slide on top of each other. This leads to the chloro-bridged structure of 2 stabilized by electrostatic interactions between Cu and Cl atoms located at different layers. Both complexes exhibit prominent catecholase activity in methanol following the oxidation of 3,5-di-tert-butyl catechol (DTBC) to the corresponding quinone. Based on the observed turn over frequency of 1 (25.19 h−1) and 2 (10.76 h−1), the monomeric complex demonstrates more catechol mimetic oxidation than the dimer. A plausible mechanism of catecholase activity has been discussed.