Synthesis, Spectral, and Cyclic Voltammetric Studies of Tetraaza Copper(II), Oxovanadium(IV), and Zinc(II) Complexes Derived from 1,2‐(Diimino‐4′‐antipyrinyl)‐1,2‐diphenylethane and para‐Substituted Anilines

Abstract

Tetraaza acyclic Schiff bases, prepared from 1,2‐(diimino‐4′‐antipyrinyl)‐1,2‐diphenylethane and p‐substituted anilines, act as tetradentate ligands and form solid cationic solid complexes with Cu(II), Zn(II), and VO(IV) salts in ethanol. Microanalytical data, magnetic susceptibility measurements, IR, UV‐VIS, mass, 1H and 13C NMR, and ESR spectral techniques were used to characterize the structures of synthesized compounds. IR and UV‐VIS spectra of the complexes suggest that all the copper complexes exhibit square–planar geometry while the oxovanadium complexes are of square–pyramidal geometry. Mass, 1H and 13C NMR spectra of the Schiff bases and their complexes suggest that the general formula of the complexes is [ML]Y (where L = L1, L2 or L3, Y = Cl2 or SO4). Electrolytic behaviour of the chelates was assessed from their higher conductance data. Monomeric nature of the chelates was confirmed from their magnetic susceptibility values. Redox studies by cyclic voltammetry of copper complexes in MeCN suggest the existence of unusual oxidation states such as Cu(III), Cu(I), and Cu(0) which are stabilized by the ligand systems. The cyclic voltammogram of the oxovanadium complexes in MeCN shows two quasi‐reversible peak for the VO(IV)/VO(V) and VO(IV)/VO(III) couples. The X‐band ESR spectra of copper and oxovanadium complexes in DMSO solution at 300 and 77 K were recorded and their salient features are discussed.