Crystal and Molecular Structures of 2,2′-bipyridine-5,5′-dicarboxylate Complexes: [M(II)(O₂CC₁₀H₆N₂CO₂)(H₂O)₄] (M = Co, Ni)

Abstract: The reaction of 2,2′-bipyridine-5,5′-dicarboxylic acid (HO₂CC₁₂H₆N₂CO₂H, H₂bpydicarb) with the appropriate metal salt in water provided the mononuclear complexes [M(II)(bpydicarb)(H₂O)₄]·2H₂O where M(II) = Co and Ni. The isomorphous materials exhibit neutral six-coordinate metal–ligand complexes with MN₂O₄ geometry. Charge balance is achieved through deprotonation of the carboxylate groups. The Co compound crystallizes in the monoclinic space group C2/c with a = 12.696(4) Å, b = 9.195(4) Å, c = 13.207(5) Å, β = 93.78(1)°; the isomorphous Ni compound exhibits cell parameters a = 12.477(4) Å, b = 9.818(3) Å, c = 12.658(4) Å, β = 92.099(6)°. Graphic Abstract: The six coordinate structure of [Co(II)(bpydicarb)(H₂O)₄] achieves charge balance through deprotonation of the carboxylate residues of the bipyridine-based ligand.[Figure not available: see fulltext.]