Abstract
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)).
Highlights
The design of coordination polymers has become an important field of crystal engineering due to their various functional properties and many possible applications, e.g., in catalysis, gas and energy storage, gas separation, magnetism, luminescence, molecular sensing, biomedical imaging [1,2,3,4,5,6,7,8]
The coordination preferences of the particular metal ions and the respective geometric and electronic properties of the ligands have been extensively studied in the past, but are still not understood completely
By properly selecting experimental parameters such as a choice of solvents, starting metal salts, additional ligands, temperature, hydrothermal conditions, pH value of the reaction mixture etc., it is possible to optimize the design of the desired coordination polymers, and control the outcome of the crystallization experiments [9,10,11,12]
Summary
The design of coordination polymers has become an important field of crystal engineering due to their various functional properties and many possible applications, e.g., in catalysis, gas and energy storage, gas separation, magnetism, luminescence, molecular sensing, biomedical imaging [1,2,3,4,5,6,7,8]. The coordination preferences of the particular metal ions and the respective geometric and electronic properties of the ligands have been extensively studied in the past, but are still not understood completely. By properly selecting experimental parameters such as a choice of solvents, starting metal salts, additional ligands, temperature, hydrothermal conditions, pH value of the reaction mixture etc., it is possible to optimize the design of the desired coordination polymers, and control the outcome of the crystallization experiments [9,10,11,12].
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