The chemical and electrochemical synthesis of trinuclear metal chelates of Cu(II), Ni(II), Co(II), Zn(II), and Cd(II) with a new tetradentate ligand system bis-[(2-oxy, -mercapto, N-tosylamino)anyls] of nitro- and phenylmalondialdehyde was carried out. Magnetic and EPR-spectral data showed that the spin-spin exchange interactions of the antiferromagnetic type between copper ions possess inner- and intermolecular character and depend on the composition of the coordination unit, the nature of the substituent in the malondialdehyde fragment, and the synthetic technique applied. (C) 2002 Elsevier Science Ltd. All rights reserved.