A novel symmetrical bis-tetradentate Schiff base, H₄L, has been prepared from the condensation of H₂L′[N,N′-bis(3-aminopropyl)oxamide] with imidazole-2-carbaldehyde. This ligand reacts with copper(II) perchlorate in neutral medium to yield the dinuclear complex [Cu₂(H₂L)][ClO₄]₂, which has two non-deprotonated imidazolyl moieties. The crystal structure of this compound, solved by single-crystal X-ray diffraction, consists of planar centrosymmetric dinuclear copper(II) cations and two perchlorate anions. The copper(II) ions are bridged by an oxamidate group in trans conformation resulting in a copper–copper distance of 5.119 Å. Each copper(II) ion occupies an inner site of the dideprotonated ligand with a CuN₃O distorted square-planar environment, and bond distances of ca. 1.95 Å. In [Cu₂(H₂L)][ClO₄]₂, each copper(II) ion can additionally accept one donor atom in axial position. Under basic conditions, this donor atom is the deprotonated imidazolate nitrogen atom from another dinuclear [Cu₂L] unit, giving rise, by a self-assembly process, to the formation of the polynuclear copper(II) complex [(Cu₂L)_n]. In this complex the copper(II) ions must be alternatively bridged by oxamidate and imidazolate groups. From magnetic susceptibility measurements, both [Cu₂(H₂L)][ClO₄]₂ and [(Cu₂L)_n] were found to exhibit strong antiferromagnetic exchange coupling, with J values of –431 and –265 cm^–1, respectively.