Coordination polymers of unsymmetrical angular ligand 3-pyridin-4-ylbenzoate acid: Syntheses, structural diversity and properties

Six new 1–3D coordination polymers of an unsymmetrical angular ligand 3-pyridin-4-ylbenzoate (L), namely, [Ni(L)2(C2H6O2)]n (1), [Cd(L)2(H2O)2]n·4H2O (2), [Zn2(OH)(L)3]n (3), [Fe2(OH)(L)3]n (4), [Ni(L)2(H2O)]n (5) and [Cd(L)2(H2O)]n (6) were hydro(solvo)thermally synthesized. They have abounding structure chemistry ranging from one-dimensional ribbons (1 and 2), and two-dimensional novel helical double-layered frameworks (3 and 4) to three-dimensional CdSO4-topological porous interpenetrating architectures with hydrophilic and hydrophobic channels regularly arraying (5 and 6). The labile conformations and coordination modes of ligand L, which were finely tuned by reaction conditions, perhaps play the key role in the construction of various architectures. Very interestingly, the slight difference in solvent system or temperature resulted in the distinct architectures of nickel(II) complexes 1 and 5 or cadmium(II) complexes 2 and 6. As expected, the unsymmetrical ligand L has a trend to construct metal-organic helixes as observed in 3 and 4. Thermogravimetric analysis of 5 shows the main framework retains stability until a higher temperature 379 °C. The 3D microporous network of 5 can slightly absorb for N2 and Ar. Compounds 2, 3 and 6 emit ligand-centered photoluminescence but with obviously different intensities owing to the structural diversities and coordinating water molecules.