Three novel oxamido-bridged heterobinuclear copper(II)-nickel(II) complexes incorporating two different tetraazamacrocyclic compounds were synthesized and characterized by IR, ESR, and electronic spectra. They are of the formulas [(CuL 1 )Ni(rac-cth)](ClO) 42´H2 O (1), [Cu(L 2 )Ni(rac-cth)](ClO 4 ) 2´0 .5 EtOH (2), and [(CuL 3 )Ni(rac-cth)](ClO 4 ) 2´H2 O (3). L 1 , L 2 , and L 3 are the dianions of diethyl 5, 6,7,8,16,17-hexahydro-6,7-dioxo-15H-dibenzo[e,n][1,4,8,12]tetraazacyclopentadecine-13,19-dicarboxylate, diethyl 5,6,7,8,15,16-hexahydro-6,7-dioxodibenzo[1,4,8,11]tetraazacyclotetracine-13,18-dicarboxylate, and diethyl 5,6,7,8,15,16-hexahydro-15-methyl-6,7-dioxodibenzo[1,4,8,11]tetraazacyclotetradecine-13,18-dicarboxylate, respectively, and rac-cth is rac-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane. The crystal structures of 1 and 2 were determined by single-crystal X-ray analysis. The Ni II ion is pseudooctahedrally coordinated. The coordination geometry around the Cu II ion in 2 is slightly distorted square planar, while that in 1 shows significant distortion towards a tetrahedral structure. The temperature dependence of the magnetic susceptibility for 1 and 2 was analyzed by means of the Hamiltonian H Ã À 2JS Ã 1´S Ã 2 , leading to J À 63.9 and À 67.4 cm À1 for 1 and 2, respectively.