Multi-dimensional transition-metal coordination polymers with 5-nitro-1,2,3-benzenetricarboxylic acid exhibiting ferro-/antiferromagnetic interactions.

Six transition metal coordination polymers, [Cu-3(nbta)(2)(bipy)(2)(H2O)(2)]center dot 2H(2)O (1), [Cu-3(nbta)(2)(bpp)(2)(H2O)(2)]center dot 2H(2)O (2), [Co-3(nbta)(2)(bipy)(3)(H2O)(2)]center dot 2H(2)O (3), [Co-3(nbta)(2)(bpp)(2)(H2O)(2)] (4), [Ni-2(Hnbta)(2)(bipy)(2)(H2O)(2)] (5) and [Ni-3(nbta)(2)(bpa)(3)(H2O)(2)]center dot 2H(2)O (6) (H(3)nbta = 5-nitro-1,2,3-benzenetricarboxylic acid, bipy = 4,4'-bipyridine, bpa = 1,2-bis(4-pyridyl) ethane, bpp = 1,3-bis(4-pyridyl) propane), have been hydrothermally synthesized by the reactions of Cu-II, Co-II and Ni-II salts with H3nbta in the presence of dipyridyl-type co-ligands, respectively. Their structures were determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, and TG analyses. Compounds 1-4 and 6 exhibit 3D pillared-layer structures while compound 5 has a 2D layer. The nbta(3-) ligands in the 2D carboxylate layer motifs of 1-4 and 6 connect transition metal ions in different coordination modes, and the dipyridyl-type co-ligands in compounds 1-4 and 6 serve as the pillar between the 2D layers, creating 3D open frameworks. From a topologic point of view, complex 1, 2 and 4 present 4-connected 3D coordination frameworks with the topologies of (4(2).6(2).8(2)) (6(2).7(2).8(2)) (4(2).6(2).7.8), (6(4).8(2)) (4(2).6(4)) (4(2).6(4)) and (4.6(4).8)(4(4).6(2))(4(3).6(3)) respectively. Complex 3 shows a (4,5)-connected 3D network with (4(2).6(7).8)(6(4).8(2))(4(2).6(4)) topology. Whereas the structure of 5 is a 2D (4,4) net due to the partially deprotonated H(3)nbta ligand existed. Complex 6 features a 3D (4,5)-connected framework with (4.6(8).8) (6(5).8) (4.6(5)) topology, also exhibiting the intriguing helical motif. The variable-temperature magnetic susceptibility studies reveal antiferromagnetic interactions between Cu-II or Co-II ions in 1, 2, 3, 4 and ferromagnetic interactions between Ni-II ions for 5 and 6, respectively.