In recent studies1,2 our attention has been focused on the investigation of the ability of the phthalate dianion (phth) to support long-range ferromagnetic interactions. It was shown that the variations in ωsthe angle between the planes of the two carboxylato groups of each phthalato intervening bridgescould play a significant role on the magnetic behavior of the complex. Moreover, it is well-known that, copper(II)phthalato complexes have been of considerable structural interest.3,4 To the best of our knowledge, however, it has been found that in almost all cases the phthalate dianion acts as a bridging ligand from both its carboxylate groups. As a consequence, almost all CuII-phthalato complexes are chain or layer-type polymers in which the phth dianion bridges the Cu ions. There has been only one case4h in which phth dianions do not act as bridging ligands, since they are involved in the discrete [Cu(phthalato)2(H2O)2] moieties, as well as another one in which they afford discrete dimeric molecules.5 However, as far as we are aware, the magnetic properties of none of the previous complexes have yet been studied, despite the fact that the transition metal coordination polymers have been the subject of intense research in the last few decades.6 Moreover, major advances have been made in both their theoretical description and their applications as new materials. Therefore, we thought it was advisable to further explore this very interesting class of compounds. To accomplish thissand contrary to previous experiments which used diethylenetriamine (dien) in the presence of the potential ligand ClO4, yielding a strongly ferromagnetically coupled complex1sdien in the presence of a less potential ligand than phth, namely CH3COO, has been used. Again we were pleased to realize that this experimental approach does work. Hence, we report herein on the synthesis, crystal structure, and interpretation of the magnetic behavior of the onedimensional, polymeric [Cu(μ-phth)(dien)]‚0.5CH3OH, (1) complex in which each phth dianion bridges the CuII ions through one of its two carboxylate groups only while its second carboxylate group remains pendant. The key point here is that 1 constitutes the first example of a chain molecule in which neither the benzene ring nor the second carboxylato group of the phth bridging dianion is involved in the intrachain magnetic exchange pathway; the second carboxylato group, however, is involved in the interchain one.