Organic–Inorganic Hybrid Coordination Polymers Based on 6-Methylpyridine-2,4-dicarboxylic Acid N-Oxide (MPDCO) Ligand: Preparations, Interpenetrating Structures, and Magnetic and Luminescent Properties

Eight novel coordination polymers based on the 6-methylpyridine-2,4-dicarboxylic acid N-oxide (MPDCO) ligand, [M(MPDCO)(H₂O)_x]_n (M = Mn²⁺, x = 1 (1); M = Cu²⁺, x = 2 (2)), [M(MPDCO)(bpy)(H₂O)·(H₂O)]_n (M = Co²⁺ (3), Ni²⁺ (4)), [M(MPDCO)(TPB)_0.5(H₂O)·(H₂O)_x]_n (M = Co²⁺(5), Ni²⁺ (6), Zn²⁺ (7), Cd²⁺ (8)) (bpy = 4,4′-bipyridine, TPB = 1,2,3,4-tetra-(4-pyridyl)-butane) have been prepared and structurally characterized. Compounds 1 and 2 are both two-dimensional (2-D) layers, which are further stacked via strong interlayer hydrogen-bond interactions to form three-dimensional (3-D) supramolecular structures. Compounds 3 and 4, which contain 3-fold interpenetrating nets, are isostructural and feature 3-D (10,3)-d open frameworks. In isomorphous compounds 5–8, 2-D sheets with nonequivalent nodes of (4²·6²·8²)(4·6²)₂ topology were constructed from metal cations, MPDCO, and the four-connecting ligand 1,2,3,4-tetra-(4-pyridyl)-butane (TPB). Then the inclined interpenetration of these 2-D sheets leads to 3-D porous architectures with rhombic channels that embody some disordered water molecules. Dominant antiferromagnetic coupling was observed in compounds 1, 3, and 4. The compounds 7 and 8 both exhibit strong fluorescent emissions in the solid state and may be suitable as candidates of blue-fluorescent materials.