Diverse Ni(II) MOFs constructed from asymmetric semi-rigid V-shaped multicarboxylate ligands: structures and magnetic properties

Novel nickel(II) coordination polymers have been constructed from asymmetric semi-rigid V-shaped multicarboxylate ligands with the help of 4,4'-bipyridine (4,4'-bpy) ligand. The hydrothermal reaction between 3-(4-carboxy-phenoxy)-phthalic acid (H3L1) and Ni(OAc)(2)center dot 4H(2)O led to the formation of [Ni-3(L-1)(2)(mu-4,4'-bpy)(3)(H2O)(2)](n)center dot(4,4'-bpy)(n)center dot(H2O)(5n) (1). In contrast, the same reaction using 3-(2-carboxy-phenoxy)-phthalic acid (H3L2) as a starting material instead of H3L1 resulted in [Ni-3(L-2)(2)(H2O)(4)(mu-4,4'-bpy)(3)](n)center dot(H2O)(2n) (2) and [Ni-3(L-2)(2)(H2O)(4)(mu-4,4'-bpy)(4)](n)center dot(H2O)(2n) (3) at 120 and 150 degrees C, respectively, revealing the effect of reaction temperature on the structure of the coordination polymer formed from the semi-rigid V-shaped ligand of L-2. Single-crystal X-ray diffraction analysis reveals that complex 1 shows a 3D framework structure assembled from right-and left-handed helices together with isolated tubes. This compound represents the first metal-organic hybrid tube constructed from an asymmetric semi-rigid V-shaped multicarboxylate ligand. Compound 2 also exhibits a 3D network composed of discontiguous trinuclear Ni(II) clusters, while the 3D architecture of 3 consisting of isolated Ni(II) ions separated in a long distance is constructed by two kinds of 2D (6,3) networks. Magnetic studies reveal the overall antiferromagnetic interaction between the neighbouring Ni(II) ions in 1-3.