Synthesis, characterisation and magnetic properties of cobalt(II) complexes with picolinic acid derivatives: the crystal and molecular structures of [Co(MeC5H3NCOO)2(H2O)2] and [CoCl2(C5H4NCOOPri)2]

The reaction of Co(AcO)2 with 6-methyl-2-pyridinecarboxylic acid, and that of CoCl2 with the isopropyl ester of 2-pyridinecarboxylic acid, both with a 1:2 metal to ligand molar ratio, afford optimum yields for the synthesis of cis-[Co(MeC5H3NCOO)2(H2O)2] and cis-[CoCl2(C5H4NCOOPri)2], respectively. According to X-ray crystallography they both consist of mononuclear discrete molecules with octahedral coordination around Co(II). The ESR powder spectra of the related Zn phases doped with 0.25% Co(II) show the strong anisotropy of the g and A tensors. The magnetic behaviour of the solid complexes is characteristic of Co(II) systems with important spin–orbit coupling and weak antiferromagnetic interactions. Electronic UV–Vis and magnetic data indicate that these complexes, as well as the already known trans-[Co(C5H4NCOO)2(H2O)2], have a high-spin octahedral geometry in solution.