New complexes of cobalt(II) ions with pyridinecarboxylic acid N-oxides and 4,4′-byp

This paper reports a study concerning the isolation and characterization of mixed ligand complexes of the Co(II) ions with pyridinecarboxylic acids N-oxides (picolinic (PNO), nicotinic (NNO) and isonicotinic (INO)), [Co(PNO)2(4,4′-byp)]·6H2O 1, [Co(NNO)(4,4′-byp)NO3]·8H2O 2 and [Co(INO)(4,4′-byp)NO3]·7H2O 3; (4,4′-byp = 4,4′-bipyridine). The complexes 2 and 3 were prepared by the hydrothermal synthesis. The structures of the complexes were elucidated on the basis of elemental analysis, thermal decomposition, IR and mass spectroscopy. IR spectra show that N-oxides act as bidentate ligands, in which both the N-oxide and the carboxylate groups are involved in coordination. In 2 and 3 the Co(II) ion exists in the same coordination environment. For 1, the X-ray crystal structure has been determined and it turned out that it contains the coordination polymers, created by the chains of Co ions joined by 4,4′-byp ligands. The Co(II) ion occupies the center of symmetry in the space group C2/c. This ion is coordinated by two nitrogen atoms (from two 4,4′-byp ligands) and four oxygen atoms from two PNO anions. The extensive network of hydrogen bonds involving six different water molecules connects the one-dimensional polymers into three-dimensional crystal structure.

► We synthesized and characterized structurally new cobalt mixed ligand complexes.
► Different ways of coordination of N-oxide ligands were studied.
► Crystal structure of [Co(PNO)2(4,4′byp)]·6H2O was determined.
► Comparison of thermal behavior of the complexes is shown.