A new three-dimensional cobalt(II) coordination polymer based on V-shaped 3,4'-oxydibenzoate: synthesis, crystal...

A new coordination polymer (CP), namely poly[(μ-4,4'-bipyridine)(μ₃-3,4'-oxydibenzoato)cobalt(II)], [Co(C₁₄H₈O₅)(C₁₀H₈N₂)]_n or [Co(3,4'-obb)(4,4'-bipy)]_n (1), was prepared by the self-assembly of Co(NO₃)₂·6H₂O with the rarely used 3,4'-oxydibenzoic acid (3,4'-obbH₂) ligand and 4,4'-bipyridine (4,4'-bipy) under solvothermal conditions, and has been structurally characterized by elemental analysis, IR spectroscopy, single-crystal X-ray crystallography and powder X-ray diffraction (PXRD). Single-crystal X-ray diffraction reveals that each Co^II ion is six-coordinated by four O atoms from three 3,4'-obb^2- ligands, of which two function as monodentate ligands and the other as a bidentate ligand, and by two N atoms from bridging 4,4'-bipy ligands, thereby forming a distorted octahedral CoN₂O₄ coordination geometry. Adjacent crystallographically equivalent Co^II ions are bridged by the O atoms of 3,4'-obb^2- ligands, affording an eight-membered Co₂O₄C₂ ring which is further extended into a two-dimensional [Co(3,4'-obb)]_n sheet along the ab plane via 3,4'-obb^2- functioning as a bidentate bridging ligand. The planes are interlinked into a three-dimensional [Co(3,4'-obb)(4,4'-bipy)]_n network by 4,4'-bipy ligands acting as pillars along the c axis. Magnetic investigations on CP 1 disclose an antiferromagnetic coupling within the dimeric Co₂ unit and a metamagnetic behaviour at low temperature resulting from intermolecular π-π interactions between the parallel 4,4'-bipy ligands.