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.

Graphical abstractTwo complexes of 2,2′-biphenyldicarboxylate (2,2′-dpa) with helical sub-structure have been synthesized. When the center metal ion is changed from Cu(II) to Ni(II), the structure is then changed from the double stranded helix to the single one, and the strong antiferromagnetic coupling interactions is then changed to weak one.Figure optionsDownload full-size imageDownload as PowerPoint slide