Synthesis of new macrobicyclic tricompartmental ligands and site preference of metal ion: structural and electrochemical properties of mononuclear copper(II) complexes

Abstract

New macrobicyclic tricompartmental ligands and their mononuclear copper(II) complexes of type [CuH 2L](ClO 4) 2 have been synthesized from the precursor compound 3,4:10,11-dibenzo-1,13[ N, N ′{bis(3-formyl-2-hydroxy-5-methyl)benzyl}diaza]-5,9-dioxa-cycloheptadecane with diamines like en, pn and bn by template method. These complexes have been characterized by IR, UV spectral and X-ray studies. Complex [CuH 2L 3](ClO 4) 2 (in L 3 the diamine used is bn) crystallized as triclinic system with space group p-1. The crystal structure explains that the geometry around copper is distorted square planar. Among the three compartments, it is interesting to observe that the metal ion prefers to be encompassed by the compartment containing phenolic oxygens and imine nitrogens (N 2O 2). From X-ray studies the presence of perchlorate anions, acetonitrile solvent molecules and the protonation of tertiary nitrogen atoms were well understood. All the complexes show hyperfine splittings in ESR spectra. The μ eff values observed in the range 1.69–1.72 BM are close to the spin only value of single copper(II) ion. Cyclic voltammetry studies of these complexes depict one electron quasireversible reduction in the range −0.80 to −0.90 V at negative potential. A red shift in UV–Visible spectra and shifting of reduction potential towards anodic in cyclic voltammetry were witnessing the distortion of the geometry around metal center from the planarity as the macrocyclic chain length in imine nitrogen compartment increases.