COPPER(II) AND COBALT(II) COMPLEXES OF PYRIDINE-2-CARBOXAMIDE AND PYRIDINE-2-CARBOXYLIC ACID

The formation constants of the following have been measured with a polarographic method: binary copper(II) complexes of pyridine-2-carboxamide (picolinamide) and pyridine-2-carboxylic acid (picolinic acid), a ternary copper(II) complex of picolinic acid and imidazole, and a binary copper(I)-imidazole complex. The larger formation constant for picolinic acid over picolinamide is ascribed to the greater chelating ability of a carboxylate group over an amide carbonyl oxygen. The crystal and molecular structure of diaquobis(picolinato)cobalt(II) dihydrate, [Co(H 2 O) 2 (pc) 2 ].2H 2 O, has been determined from three-dimensional MoKα X-ray collected by the multiple-film Weissenberg method. The unit cell dimensions are: a=9.89 ± 0.02 A, b=5.17 ± 0.01 A, c=17.50 ± 0.06 A, β=123.8 ± 0.4°. The space group is P2 1 /c, and the calculated density is 1.67 g cm −3 with two formula weights per cell. The measured density is 1.67 g cm −3 . The structure was solved by the Patterson method and refined by a least-squares method. With a total of 1659 observed independent reflections, the final R factor is 10.2% without the hydrogens and 9.7% with the hydrogens. The two picolinate groups are planar and related by an inversion center at the cobalt atom. The cobalt atom is coordinated by a distorted octahedron formed by the two nitrogens of the pyridine rings, two oxygens from the carboxyl groups, and two oxygens of coordinated water molecules. The molecules are hydrogen-bonded into layers parallel to the be plane. Between adjacent layers, only van der Waal's contacts are observed.