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

This paper describes the synthesis of the Zn(II) complex with H2L = 2-hydroxyiminopropanoic acid. The final structure incorporated two linear dimeric anions with two Zn2+ atoms, which are linked by a carbonate anion into a tetranuclear unit. In each dinuclear unit, the two Zn(II) ions are coordinated by three molecules of the doubly deprotonated ligand in two different coordination modes. This result is confirmed both by X-ray crystallography and by ESI-MS investigations of the crystals dissolved in water. Equilibrium studies of the zinc(II) complexes formed by H2L in aqueous solution based on independent pH-metric titrations and zinc ion-selective electrode (ISE) titrations indicate that the mononuclear ZnLH complex appears to be the dominating equilibrium species at pH 4–6 at various ligand-to-metal ratios. Under excess of the ligand at pH 6–8, the ZnL2H species, further stabilized by a hydrogen bond between the deprotonated and protonated oxime groups, becomes the predominating species besides the ZnL complex.

Synthesis yielded a complex in which two linear dimeric anions have two Zn2+ atoms linked by the carbonate anion into a tetranuclear unit. The predominating species in aqueous solution are mononuclear: ZnLH (pH 4–6) and ZnL, ZnL2H (pH 7–8) with an intramolecular H-bridge between the oxime oxygens.Figure optionsDownload as PowerPoint slide