Compartmental unsymmetrical lateral macrobicyclic ligands with an aromatic backbone providing a phenoxo bridge: synthetic, spectral, magnetic, electrochemical and kinetic features of mono and binuclear copper(II) complexes

Abstract

From macrobicyclic ligands having different compartments originated from their corresponding precursor compounds (PC-1: 3,4:9,10-dibenzo-1,12[ N, N ′-bis{(3-formyl-2-hydroxy-5-methyl)benzyl}diaza]-5,8-dioxacyclotetradecane and PC-2: 3,4:9,10-dibenzo-1,12[ N, N ′-bis{(3-formyl-2-hydroxy-5-methyl)benzyl}diaza]-5,8-dioxacyclopentadecane) several mono and binuclear copper(II) complexes denoted as [CuL](ClO) 4 and [Cu 2L(ClO 4)](ClO 4) have been synthesized. Electrochemical studies vindicate that one quasireversible reduction wave ( E pc=−0.80 to −0.88 V) for the mononuclear complexes and two quasireversible one electron transfer reduction waves ( E pc 1=−0.84 to −0.94 V, E pc 2=−1.25 to −1.40 V) for the binuclear complexes are obtained in the cathodic region. The probe of room temperature magnetic moment studies depicts the presence of an antiferromagnetic interaction in the binuclear complexes ( μ eff of 1.35–1.42 B.M.), which is also observed from the broad ESR spectra with a g value of 2.10 or 2.11. Whereas, hyperfine splitting in ESR spectra is observed for mononuclear complexes and the magnetic moment value is found to be close to the spin only value ( μ eff of 1.69–1.71 B.M.). A variable temperature magnetic susceptibility study of the complex was carried out and the calculated −2 J values for the binuclear complexes [Cu 2L 1a(ClO 4)](ClO 4) and [Cu 2L 1b(ClO 4)](ClO 4) are 240 and 219 cm −1, respectively. The initial rate constant values of catechol oxidation using the complexes as catalysts have been found to span a domain ranging from 5.06 × 10 −3 to 2.56 × 10 −2 min −1 and the values are found to be higher for binuclear complexes than the corresponding mononuclear complexes. Spectral, electrochemical and catalytic studies support the distortion of the copper ion geometry that arises as the macrocyclic ring size increases.