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 P_r = 0.0188 μC cm⁻², coercive field E_c = 9 kV cm⁻², saturation of the spontaneous polarization P_s = 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.