Biphenyl-2,4,6,3′,5′-pentacarboxylic acid as a tecton for six new Co(ii) coordination polymers: pH and N-donor ligand-dependent assemblies, structure diversities and magnetic properties

Abstract

Six new Co(II)-based mixed-ligand coordination polymers, namely, [Co₂(H₃bppc)₂(2,2′-bpy)₄]·H₂O (1), [Co₂(Hbppc)(2,2′-bpy)₂(H₂O)]·H₂O (2), [Co(H₂bppc)(H-bpp)]·2H₂O (3), [Co₃(μ₃-OH)(bppc)(dps)(CH₃CH₂OH)]·4H₂O (4), [Co₂(bppc)(bib)(H₂O)₄]·(H₂-bib)_0.5·(H₂O)₃ (5), and [Co₂(Hbppc)(bix)₂]·2H₂O (6), (H₅bppc = biphenyl-2,4,6,3′,5′-pentacarboxylic acid, 2,2′-bpy = 2,2′-bipyridine, bpp = 1,3-bis(4-pyridyl)propane, dps = 4,4′-sulfanediyldipyridine, bib = 1,4-bis(imidazol-1-yl)benzene, bix = 1,4-bis(imidazol-1-ylmethyl)benzene), have been obtained under solvothermal conditions. 1 exhibits a 3D supramolecular framework based on a [Co₂(H₃bppc)₂(2,2′-bpy)₄] unit. 2 has a (3,4)-connected dmc net with a (4·8²)(4·8⁵) topology containing alternate binuclear metal clusters and single metal centres. 3 shows a 3D supramolecular architecture constructed from ladder-like arrays decorated with H-bpp. 4 exhibits a binodal (5,7)-connected 3D network based on trinuclear [Co₃(μ₃-OH)]⁵⁺ units with an unusual (3·4⁶·5²·6)(3²·4⁶·5⁷·6⁵·7) topology. 5 features a (4,6)-connected 3D fsc open framework with binuclear [Co₂(H₂O)(COO)]³⁺ units as nodes, and H₂-bib and water molecules located in the voids of its framework by hydrogen bonds. 6 possesses a 3D net containing unusual 2D polyrotaxane sheets. Topological analysis reveals that 6 has a (3,4,4)-connected 3D network with a (4·6·7⁴)(4·6·7)(6·7²·10²·11) topology. The structural difference of 1 and 2 is due to the different pH values of the reaction system. Though complexes 2–6 were synthesised under similar reaction conditions, the carboxylic groups of H₅bppc were partially deprotonated in 2, 3 and 6 and fully deprotonated in 4 and 5. Complexes 2–6 display diverse structures depending on different N-donor ligands and the coordination modes of the multicarboxylate ligand. Variable-temperature magnetic susceptibility measurements reveal that complexes 1–6 show antiferromagnetic interactions.