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Two series of dicopper(II) complexes derived from bis( N- salicylidine)dicarboxylic acid dihydrazides (H 4 L n ) of general formula [Cu 2 (L n )· x H 2 O]· y H 2 O and [Cu 2 (H 2 L n )Cl 2 · x H 2 O]· y H 2 O 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 [Cu 2 (L n )· x H 2 O]· y H 2 O indicate significant antiferromagnetic coupling between copper(II) centers. The -2 J 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 [Cu 2 (H 2 L n )Cl 2 · x H 2 O]· y H 2 O with n = 0, 2 and 3 also show strong antiferromagnetic exchange coupling (-2 J = 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 (-2 J = 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. [ABSTRACT FROM AUTHOR]