Eight new coordination polymers containing rigid 4-(4-carboxy-phenyl)-pyridine-2-carboxylic acid: Synthesis, structural diversity, fluorescence and magnetic properties

Abstract

Eight new coordination polymers (CPs) were successfully synthesized through the solvo-thermal reactions of H2cppc ligand and a series of transition metal salts, [M(cppc)(H2O)2]n [M = Co, (1); Ni, (2); Zn, (3); Cd, (4)], [M(Hcppc)2]n [M = Cd, (5); Mn, (6); Cu, (7)], [Pb(cppc)(H2O)]n (8), [H2cppc = 4-(4-carboxy-phenyl)-pyridine-2-carboxylic acid]. These compounds were all characterized by elemental analysis, IR spectra, single-crystal X-ray diffraction, powder X-ray diffraction and thermal analysis. Compounds 1–4 have similar molecular formula except for different metal centers, notably, compounds 1–3 with isomorphic frameworks display two-dimensional layer structure, in which contain left- and right-handed chiral chains constructed from M2(H2O)2 dimers and cppc2− anions. However, compound 4 exhibits a three-dimensional network with Cd-O-Cd inorganic chains, different from that of compounds 1–3. Compounds 5–7 also have similar molecular formula except for different metal centers, the isomorphic compounds 5 and 6 exhibit two-dimensional undulating layers, while compound 7 displays one-dimensional chain. Compound 8 is a 2D layer structure with Pb2O2 secondary building units. In general, coordination geometries of metal centers and coordination modes of the ligands have an important effect on the structures of targeted compounds. Fluorescent experiments indicate that compounds 3–5 and 8 display apparently blue light emission in the solid state. Magnetic properties of compounds 1, 2, 6 and 7 are also investigated.