Synthesis, Crystal Structures, and Properties of a Series of Coordination Polymers Employing R4-Terephthalate (R = H, F, Cl, Br) and 4,4′-Bipyridine as Bridging Ligands

We report on the synthesis, single-crystal structures, and properties (IR, UV-vis, ESR, and TG) of a series of coordination polymers employing R-4-terephthalate dianion (R-4-benzenedicarboxylate dianion, R-4-bdc(2-): R = H, F, Cl, Br) in which halogen atoms are systematically changed and 4,4'-bipyridine (4,4'-bpy) as cobridging ligands. These compounds are synthesized under the same conditions and all display octahedral metal coordination environments. A one-dimensional coordination polymer, [Mn(mu-4,4'-bpy)(H2O)(4)](H-4-bdc) (1) consists of Mn(II) and 4,4'-bpy was obtained by reaction of Mn(II), terephthalate and 4,4'-bpy. Uncoordinated terephthalate acts as not only counter ion but also linker to form a three-dimensional network by hydrogen-bonding and pi-pi interactions. When halogen atoms are introduced to a benzene ring, layers of square-grid of octahedral Mn(II) ions are obtained for [Mn(mu-F-4-bdc)(mu-4,4'-bpy)(H2O)(2)] (2), [Mn(mu-Cl-4-bdc)(mu-4,4'-bpy)(H2O)(2)] (3), and [Mn(mu-Br-4-bdc)(mu-4,4'-bpy)(H2O)(2)] (4). One of the major differences of the structures is hydrogen-bonding interactions between layers. This major difference is due to the different ionic radii of halogen atoms attached to benzene rings of the ligand to give different crystal packing. Compounds 2-4 exhibit different thermal behavior. While the XRD pattern of 2 indicates structural change upon hydration/dehydration, XRD patterns of 4 are not globally changed in these processes.