Studies on Metal Carboxylates. Part II. Cobalt(II) and Nickel(II) Complexes of Certain Pyridine Carboxylic Acids and Pyridine-3-Sulfonic Acid: Magnetic and Spectral Studies

Several pyridine carboxylate complexes of cobalt(II) and nickel(II) have been prepared and their spectral and magnetic properties and X-ray powder patterns used to establish their stereochemistry. The cobalt(II) complex of pyridine-3-carboxylic acid Co[3-py(CO2)]2•4H2O, whose crystal structure we have previously reported, was used as a model for a consideration of the structural details of these complexes. Like the latter cobalt(II) derivative, the nickel(II) complex of pyridine-3-carboxylic acid and the cobalt(II) and nickel(II) complexes of pyridine-4-carboxylic acid and pyridine-3-sulfonic acid, isolated as their tetrahydrates, are formulated as non-classical zwitterions. Comparisons are made with the related pyridine carboxylate complexes of silver(II).