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Structural and Electrochemical Studies of Cobalt(II) and Nickel(II) Coordination Polymers with 6-Oxonicotinate and 4,4′-Bipyridine

The 6-oxonicotinate (6-Onic) salts of a one- dimensional cationic cobalt(II) or nickel(II) coordination polymers with 4, 4′-bipyridine (4, 4′- bpy), namely {; ; [Co(4, 4′-bpy)(H2O)4](6-Onic)2·2H2O}; ; n (1) and {; ; [Ni(4, 4′-bpy)(H2O)4](6-Onic)2·2H2O}; ; n (2), were prepared hydrothermally by reactions of cobalt(II) nitrate hexahydrate or nickel(II) nitrate hexahydrate, respectively, 6- hydroxynicotinic acid and 4, 4′-bipyridine in a mixture of ethanol and water. In the hydrogen-bonded frameworks of 1 and 2, the one-dimensional polymeric chains of {; ; [M(4, 4′-bpy)(H2O)4]2+}; ; n (M = Co, Ni), the 6- oxonicotinate anions and the lattice water molecules were assembled via strong intermolecular O–H···O and N– H···O hydrogen bonds and π–π interactions, leading to the formation of the representative hydrogen- bond ring motifs: trimeric R23(10) motif, the centrosymmetric tetrameric R24(8) and R24(12) motifs and the pentameric R45(12) motif. The isostructural coordination polymers 1 and 2 exhibited a different electrochemical behavior, as observed by cyclic voltammetry, which can be attributed to the nature of the metal ions (cobalt(II) vs. nickel(II)).

coordination polymers ; cobalt(II) ; nickel(II) ; 6-hydroxynicotinate ; 4, 4′-bipyridine ; hydrogen-bond motifs ; cyclic voltammetry

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