Synthesis, characterization and magnetochemical studies of dicopper(II) complexes derived from bis(N-salicylidene)dicarboxylic acid dihydrazides

Abstract

Two series of dicopper(II) complexes derived from bis(N-salicylidine)dicarboxylic acid dihydrazides (H4L n ) of general formula [Cu2(L n )·xH2O]·yH2O and [Cu2(H2L n )Cl2·xH2O]·yH2O have been synthesized and characterized, where n refers to the number of carbon atoms in the aliphatic spacer between the two N-salicylideneacylhydrazine units. Magnetic susceptibility measurements for neutral dicopper(II) complexes [Cu2(L n )·xH2O]·yH2O indicate significant antiferromagnetic coupling between copper(II) centers. The −2J values obtained from the Bleany–Bowers equation are within the range 121–223 cm−1, suggesting association of the coordinated copper(II) units Cu(ONO) via phenoxy bridges. This leads to a polynuclear structure in which the dimeric units are connected with the aliphatic spacer. From the best-fit values of the mole fraction of paramagnetic uncoupled copper(II) centers (ρ), the degree of association in these polynuclear copper(II) complexes has been estimated. The chloro dicopper(II) complexes [Cu2(H2L n )Cl2·xH2O]·yH2O with n = 0, 2 and 3 also show strong antiferromagnetic exchange coupling (−2J = 215–423 cm−1), suggesting a polynuclear structure in which the copper(II) is in a distorted square-pyramidal environment, bound in the equatorial plane with a monoanionic ONO tridentate acylhydrazone unit and the μ-phenoxy oxygen and the axial site occupied by a chloride. The dicopper(II) complexes with n = 1 and 4 show weak antiferromagnetic exchange coupling (−2J = 16–20 cm−1). In these complexes the chloride ion may occupy the fourth equatorial site while the μ-phenoxy is in the apical position.