Bringing 5-(3,4-dicarboxylphenyl) picolinic acid to crystal engineering research: hydrothermal assembly, structural features, and photocatalytic activity of Mn, Ni, Cu, and Zn coordination polymers

5-(3,4-Dicarboxylphenyl) picolinic acid (H(3)dppa) was applied as a novel tricarboxylic acid block with phthalate and picolinate functionalities for the aqueous-medium assembly of seven new coordination compounds, namely, [Mn-2(mu-Hdppa)(2)(phen)(2)(H2O)(2)] (1), {[Mn(mu-Hdppa)(2,2'-H(2)biim)(H2O)]center dot H2O} n (2), [Ni(Hdppa)(phen)(2)]center dot 4H(2)O (3), {[Ni(mu-Hdppa)(mu-4,4'-bipy)center dot H2O)]center dot H2O}(n) (4), {[Cu3(mu 3-dppa)(mu-Hdppa)(phen)(4)](2)-[Cu(mu-Hdppa)(2)]center dot 10H(2)O}(n) (5), {[Ni-3(mu-dppa)(2)(mu-1,4-bpb)(2)(H2O)(6)]center dot 4H(2)O}(n) (6), and {[Zn-3(mu 4-dppa)(2)(phen)(2)(H2O)(2)]center dot 4H2O}(n) (7). These products 1-7 represent the first structurally characterized examples of the coordination compounds derived from H(3)dppa. Compounds 1-7 were assembled in the presence of various N-donor supporting ligands acting as crystallization mediators, which were selected from 1,10phenanthroline (phen), 2,2'-biimidazole (H(2)biim), 4,4'-bipyridine (4,4'-bipy), or 1,4-bis.pyrid-4-yl) benzene (1,4-bpb). Full characterization of 1-7 by IR spectroscopy, thermogravimetric (TGA), elemental, and topological analyses, as well as powder (PXRD) and single-crystal X-ray diffraction, was performed. The structural types range from the discrete 0D complexes (1 and 3) and 1D coordination polymers with a 2C1 topology (2, 5, and 6) to the 2D metal-organic layers with an sql topology (4 and 7). The structural diversity of 1-7 is driven by various factors, including the metal(II) node nature, deprotonation degree of H(3)dppa, or type of crystallization mediator. The magnetic properties of 1, 2, 4, and 6 were studied and modeled, revealing antiferromagnetic (in 1, 2, and 6) or ferromagnetic (in 4) interactions between adjacent metal(II) centers. The luminescence of 7 was also investigated. Moreover, the photocatalytic activity of 1-7 was studied for the degradation of methylene blue as a model dye pollutant, disclosing that the nickel(II) coordination polymer 4 is the most active catalyst. The observed catalytic activity of 1-7 correlates well with their band gap energies determined by the UV-diffuse reflectance method.