Synthesis, solid state and solution studies of cobalt(II) complexes with 2-hydroxyiminopropanoic acid

By using a synthetic approach alternative to the ones described up to now two tri- and tetranuclear mixed valence Co(II,III) complexes have been obtained ([Li(H2O)4]2[Co(CoL3)2(Li(H2O)3)2] and K[Co(CoL3)2Co(H2O)5]·H2O, respectively) in which the cobalt ions are linked by (N–O) oxime bridges. For both these compounds, a hydrazide derivative (2-hydroxyiminopropanehydrazide, HPH) has been used as starting ligand and then it underwent hydrolytical decomposition to 2-hydroxyiminopropanoic acid, H2L, ion upon coordination with cobalt. Cobalt(II) complexes formed by 2-hydroxyiminopropanoic acid in aqueous solution have been studied using independent pH-metric titrations as well as a combination of fibre-optics UV–Vis spectroscopy and pH glass-electrode potentiometry. The mononuclear CoL2H complex appeared to be the dominating equilibrium species within pH 6–9, most probably due to a hydrogen bond between the deprotonated and protonated oxime groups stabilizing planar cis-coordination.

Graphical abstractBy using a hydrazide derivative (2-hydroxyiminopropanehydrazide) of 2-hydroxyiminopropanoic acid as starting ligand one may obtain tri- and tetranuclear mixed valence Co(II,III) complexes in which the cobalt ions are linked by (N–O) oxime bridges.The dominating species in aqueous solution is a mononuclear CoL2H with an intramolecular H-bridge between oxime oxygens.Figure optionsDownload full-size imageDownload as PowerPoint slide