Co(II) Metal-Organic Frameworks (MOFs) Assembled from Asymmetric Semirigid Multicarboxylate Ligands: Synthesis, Crystal Structures, and Magnetic Properties

A series of four new coordination polymers, namely, [Co(HL1)(mu-4,4'-bpy)(H2O)(3)](n)center dot(4,4'-bpy)(n)center dot(H2O)(2n) (1), [Co-1.5(L-2)(mu-4,4'-bpy)(1.5)](n)center dot(4,4'-bpy)(0.5n)(2), [Co-3(L-3)(HL3)(OH)(H2O)(2)(mu-4,4'-bpy)(2)](n)center dot(H2O)(2.5n) (3), and [Co-1.5(L-4)(mu-4,4'-bpy)(2)-(H2O)(3)](n)center dot(H2O)(3n) (4), have been assembled from four asymmetric semirigid multicarboxylate ligands 3-(4-carboxy-phenoxy)-phthalic acid (H3L1), 3-(2-carboxy-phenoxy)-phthalic acid (H3L2), 4-(2-carboxy-phenoxy)-phthalic acid (H3L3), and 4-(4-carboxy-phenoxy)-phthalic acid (H3L4) With the help of 4,4'-bipyridine (4,4'-bpy) ligand. X-ray single crystal diffraction analysis reveals that compound 1 displays a one-dimensional (1D) zigzag chain structure constructed from 4,4'-bpy ligands and partly deprotonated L-1 ligands, which further forms a three-dimensional (3D) supramolecular architecture via hydrogen bonds. Complex 2 possesses a two-dimensional (2D) layered architecture composed of continuous trinuclear Co(II) clusters. Complex 3 also shows a 2D molecular framework assembled from alternate tetranuclear and dinuclear Co(II) clusters bridged by 4,4'-bpy or L-3 ligands, and complex 4 exhibits a 3D (4,4)-connected self-penetrating network constructed from ladder-like and fish bone-like subunits. Magnetic studies indicate the spin-orbit coupling of isolated Co(II) in 1 and the overall antiferromagnetic interaction in 2-4.