Six Cu(II)dimers, [{Cu(dien)} 2 (μ-dicyd)][CF 3 SO 3 ] 2 (1), [{Cu(dien)} 2 (μ-Me 2 dicyd)][CF 3 SO 3 ] 2 (2), [{Cu(dien)} 2 (μ-Cl 2 dicyd)][CF 3 SO 3 ] 2 (3), [{Cu(L)} 2 (μ-dicyd)] (4), [{Cu(L)} 2 (μ-Me 2 dicyd)] (5), and [{Cu(L)} 2 (μ-Cl 2 dicyd)] (6), where dicyd 2− , Me 2 dicyd 2− and Cl 2 dicyd 2− are unsubstituted, 2,5-dimethyl- and 2,5-dichloro-1,4-dicyanamidobenzene dianions, respectively, dien is diethylenetriamine, and L − = 1,3-bis(2-pyridylimino)isoindolinato, have been synthesized and characterized by elemental analysis, IR, UV–vis, and EPR spectroscopy, and magnetic studies. Temperature-dependent magnetic susceptibility measurements of the complexes 1–6 from 5 to 300 K are reported. The data for 2, 3, 5, and 6 have been fitted to a dimer model with a modified Bleaney–Bowers expression which derived antiferromagnetic exchange constants −J = 10.6, 4.5, 5.2, and 3.0 cm −1 , respectively (where the Hamiltonian is of the form [Formula: see text]) For 4, an approach to a maximum in χ m with decreasing temperature gave an estimated −J < 3.5 cm −1 . Only complex 1 showed Curie–Weiss behavior. This is far weaker antiferromagnetic exchange compared to that observed for dinuclear Ru(III) complexes incorporating the dicyd 2− bridging ligands (J. Am. Chem Soc. 114, 5130 (1992)) and is attributed to a symmetry and energy mismatch between Cu(II) σ* magnetic orbitals and the π nb molecular orbitals of the bridging ligand which are important for superexchange. Keywords: superexchange, copper dimer, dicyanamidobenzene.