Four cobalt(II) complexes constructed from a butterfly-shaped tetracarboxylic acid with N-donor ligands: Structures, magnetism and influence of coordination modes on dihedral angles

Four coordination complexes based on (1,1′,2′1″-terphenyl)-4,4′4″,5′-tetracarboxylic acid (H4ttac), {[Co2(H2ttac)2(H2O)5]·(H2O)10}n (1), [Co2(ttac)(pyridine)(H2O)3]n (2), {[Co2(ttac)(4,4′-bipy)1.5(H2O)]·(H2O)}n (3), and {[Co3(ttac)2(bpe)3(H2O)2]·(H2O)6}n (4), (bpe = 1,2-bis(4-pyridyl)ethene, 4,4′-bipy = 4,4′-bipyridine), have been hydrothermally synthesized and structure characterization. Complex 1 exhibits a one-dimension chain with a cavity of 12.75 × 12.84 Å2, and further stacks into a 3D framework through hydrogen bonds. 2 forms a (4,6)-connected 2D layer with the symbol of (32.42.5.6)2(32.46.52.64.7). 3 Is a 3D (4,4,4,5)-connected framework with the Schlafli symbol of (42.6.82.10)2(42.63.85)2(62.83.12)2. 4 displays a 2D double-layered grid with trinuclear units to construct a (4,4,6)-connected net marking the symbol of (4.84.12)2(43.62.8)2(44.62.88.12). The study on dihedral angles between the two monocarboxylic benzene rings in H4ttac ligands in complexes 1–4 shows that the change of dihedral angles from 62.85°, 66.24°, 56.41° to 59.69° mainly originated from the coordination numbers of their monocarboxylic groups from 3, 4, 2 to less than 2. Temperature-dependent magnetism susceptibility measurements show a ferromagnetic behavior for complex 4 and antiferromagnetic characters for complexes 1–3.

Four cobalt complexes constructed from a butterfly-shaped tetracarboxylic acid represent various dimensions and topologies, providing a study between coordination modes and dihedral angles, and complex 4 is an example of weak ferromagnetic compounds.Figure optionsDownload as PowerPoint slideHighlights
► Tetracarboxylic acid is used to build complexes for various coordination modes.
► Four cobalt complexes were successfully synthesized with hydrothermal method.
► Dihedral angles are affected by the coordination numbers of carboxylic groups.
► Complex 4 displays a weak ferromagnetic behavior.