New pyridine-2,4,6-tricarboxylato coordination polymers: Synthesis, crystal structures and properties

Abstract

Three new pyridine-2,4,6-tricarboxylic acid (H3ptc) complexes, [Mn3(ptc)2(H2O)9]n (1), [Co3(ptc)2(H2O)2]n (2), and [Co(bpy)(H2O)4]n[Co(ptc)(H2O)]2n (3) were hydrothermally synthesized and characterized by single-crystal X-ray diffraction methods, elemental analyses, IR spectroscopy, thermal analyses and magnetic measurements along with ferroelectric measurement for 1 were carried out. Compound 1 crystallizes in the acentric space groupCc and exhibits significant ferroelectricity (a remnant polarization Pr = 0.0188 μC cm−2, coercive field Ec = 9 kV cm−2, saturation of the spontaneous polarization Ps = 0.1326 μC cm−2). To the best of our knowledge, 1 represents the first example of a pyridine-2,4,6-tricarboxylato coordination polymer that exhibits possible ferroelectric behavior. Within 1, both seven- and six-coordinated Mn2+ ions are bridged by ptc3− anions to generate 1D bands, which are assembled into a 3D supramolecular architecture through extensive hydrogen bonds. The CoN2O4 and CoO6 octahedra in 2 are corner-shared to form 2D sigmoid layers, which are further interconnected by organic linkers into topologically 3D MOF of (32·46·56·6)2(32·48·512·66) type. The six-coordinated Co2+ ions in 3 are bridged by bpy and ptc ligands to give polymeric 1∞[Co(bpy)(H2O)4]2+ chains and 1∞[Co(ptc)(H2O)]1− chains, respectively, and the extensive hydrogen bonds are responsible for the construction of the 3D supramolecular architecture. Additionally, the ptc ligand exhibits two unprecedented coordination modes η5μ2 and η5μ3. The magnetic measurements of 1–3 show overall antiferromagnetic interactions between the metal ions.