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 & PRIME;-bipyridine (4,4 & PRIME;-bpy), namely {[Co(4,4 & PRIME;-bpy)(H2O)(4)](6-Onic)(2)& BULL;2H(2)O}(n) (1) and {[Ni(4,4 & PRIME;-bpy)(H2O)(4)](6-Onic)(2)& BULL;2H(2)O}(n) (2), were prepared hydrothermally by reactions of cobalt(II) nitrate hexahydrate or nickel(II) nitrate hexahydrate, respectively, 6-hydroxynicotinic acid and 4,4 & PRIME;-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 & PRIME;-bpy)(H2O)(4)](2+)}(n) (M = Co, Ni), the 6-oxonicotinate anions and the lattice water molecules were assembled via strong intermolecular O-H & BULL;& BULL;& BULL;O and N-H & BULL;& BULL;& BULL;O hydrogen bonds and pi-pi interactions, leading to the formation of the representative hydrogen-bond ring motifs: trimeric R-3(2)(10) motif, the centrosymmetric tetrameric R-4(2)(8) and R-4(2)(12) motifs and the pentameric R-5(4)(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)).

Automated summary

The study synthesized novel cobalt(II) and nickel(II) coordination polymers containing 6-oxonicotinate salts and 4,4'-bipyridine, forming crystal structures through hydrogen bonds and pi-pi interactions. The electrochemical behavior of the isostructural coordination polymers 1 and 2 differed due to the nature of the metal ions (cobalt(II) versus nickel(II)).