Magnetic investigation of two helical frameworks derived from mixed ligands

Although the 2,2′-biphenyldicarboxylate ligand (2,2′-dpa) has been widely used to construct metal-organic frameworks (MOFs) with helical sub-structure, the effect of the helical arrangement of spin carriers on the magnetic properties remains rarely scarce. In this article, two unique magnetic metal-organic supramolecular frameworks with different structural features, [Cu2(dpa)2(H2O)2(4,4′-dpdo)0.5]n (1) and [Ni(H2O)4(dpa)] · (4,4′-dpdo)(H2O) (2) (dpdo = 4,4′-dipyridine-N,N′-dioxide), have been isolated from the direct reaction of H2dpa with their corresponding salts in the presence of dpdo. In complex 1, the Cu–dpa double-helical chains, which are bridged by long flexible μ2-dpdo ligands to give rise to a regular 63 covalent layer, exhibit strong antiferromagnetic coupling interactions. Whereas the 1D [Ni(dpa)]n helical chains in complex 2 exhibit weak antiferromagnetic coupling interactions. Rich hydrogen bonds between perpendicular 1D [Ni(dpa)]n helical chains and quasi-1D (dpdo)n chains result in an intricate 3D supramolecular network.