Synthesis of mono and binuclear copper(II) complexes using new macrobicyclic tricompartmental unsymmetrical ligands: magnetic, electrochemical and catalytic studies

Abstract

A series of new mono and binuclear copper(II) complexes [CuL 1a–eH 2](ClO 4) 2 and [Cu 2L 1a–e(ClO 4)](ClO 4), where L is a macrobicyclic tricompartmental ligand obtained from the condensation of the precursor compound (PC) 3,4:10,11-dibenzo-1,13[ N, N ′-bis{(3-formyl-2-hydroxy-5-methyl) benzyl}diaza]-5,9-dioxocyclohexadecane with various diamines have been synthesized. In this system, there are three compartments: the first compartment (N 2O 2) comprises two ether oxygens and two tertiary nitrogens, the second compartment (N 2O 2) contains two tertiary nitrogens and two phenolic oxygens and the third compartment (N 2O 2) is composed of two phenolic oxygens and two imine nitrogens. In mononuclear complexes the geometry of copper(II) ion present in the phenolic oxygen and imine nitrogen compartment is distorted square planar and in binuclear complexes the geometry of Cu(II) ion present in imine nitrogen and phenolic oxygen compartment is distorted square planar and the another Cu(II) ion present in phenolic oxygen and tertiary nitrogen compartment is square pyramidal. The synthesized complexes were characterized by spectroscopic (IR, UV–Vis and ESR) techniques. Electrochemical studies of the complexes reveal that all the mononuclear copper(II) complexes show a single quasireversible one-electron transfer reduction wave ( E pc=−0.76 to −0.84 V) and the binuclear complexes show two quasireversible one-electron transfer reduction waves ( E 1 pc=−0.86 to −1.01 V, E 2 pc=−1.11 to −1.43 V) in the cathodic region. The ESR spectra of the mononuclear complexes show four lines with nuclear hyperfine splittings with the observed g ∥ values in the range 2.20–2.28, g ⊥=2.01–2.06 and A ∥=125–273. The binuclear complexes show a broad ESR spectra with g=2.10–2.11. The room temperature magnetic moment values for the mononuclear complexes are in the range [ μ eff =(1.70 to 1.72) BM] and for the binuclear complexes the range is [ μ eff =(1.46 to 1.59) BM]. Variable temperature magnetic susceptibility study of the binuclear complex [Cu 2L 1d(ClO 4)](ClO 4) shows that the observed −2 J value is 225 cm −1. The calculated initial rate constant values for oxidation reaction of catechol to o-quinone ranges from 8.52 × 10 −3 to 3.08 × 10 −2 min −1. The catalytic activity of binuclear copper(II) complexes (1.65 × 10 −2 to 3.08 × 10 −2 min −1) is higher than the mononuclear copper(II) complexes (8.52 × 10 −3–9.67 × 10 −3 min −1).