Exploring biphenyl-2,4,4′-tricarboxylic acid as a flexible building block for the hydrothermal self-assembly of diverse metal–organic and supramolecular networks†
Abstract
Biphenyl-2,4,4′-tricarboxylic acid (H3btc) was applied as a principal but still little explored building block for the synthesis of nine new coordination compounds, namely, [Zn(H2btc)(phen)2][H2btc]·H2O (1), [M(H2btc)2(H2biim)2] {M = Co (2) and Cd (3)}, [Ni(Hbtc)(phen)2(H2O)]·2H2O (4), [Cd2(μ4-btc)(μ2-Cl)(phen)2]n (5), [Ni3(μ4-btc)2(μ2-H2O)2(py)4(H2O)2]n (6), {[Co3(μ4-btc)2(μ2-H2O)2(py)4(H2O)2]·(py)2}n (7), {[Co3.5(μ6-btc)2(μ3-OH)(py)2(H2O)3]·H2O}n (8), and {[Pb3(μ6-btc)2(H2O)]·H2O}n (9). These products were easily generated by a hydrothermal self-assembly method from the corresponding metal(II) chlorides, H3btc, and various N-donor ancillary ligands, selected from 1,10-phenanthroline (phen), 2,2′-biimidazole (H2biim), or pyridine (py). Compounds 1–9 were characterized by IR spectroscopy, elemental, thermogravimetric, powder and single-crystal X-ray diffraction analyses. Their structures range from the intricate 3D metal–organic frameworks (MOFs) 6–9 to the 2D coordination polymer 5 and the discrete 0D monomers 1–4. Such a structural diversity is guided by the type of metal(II) node, level of the deprotonation of biphenyl-2,4,4′-tricarboxylic acid, and kind of ancillary ligand. The structures of 1–4 are further extended [0D → 2D (1) and 0D → 3D (2–4)] into various H-bonded networks. Both the supramolecular (in 1–4) and coordination (in 5–9) underlying networks were classified from the topological viewpoint, disclosing the distinct 4,5L64 (in 1), pcu (in 2 and 3), sxb (in 4), hcb (in 5), and wei (in 6 and 7) topological nets, whereas topologically unique frameworks were identified in MOFs 8 and 9. The magnetic (for 6–8) and luminescence (for 1, 3, 5, and 9) properties were also studied and discussed.