The complexing properties of oxalodihydrazide, acethydrazide and formic hydrazide with Cu(II) in aqueous solution

Abstract Hydrazides and their solid complexes demonstrate biological and pharmacological activity. The present study determines the hitherto undescribed coordinating properties of three hydrazides (acethydrazide, formic hydrazide and oxalodihydrazide) towards copper(II) in aqueous solutions by means of various potentiometric (ISE, pH-metric) and spectroscopic (UV–Vis, EPR) methods. The speciation models are than confirmed by ESI-MS. Due to metal-promoted deprotonation, the complexes are formed below pH 2 and coordination occurs with one, two or three ligand molecules. EPR spectroscopy revealed bidentate {N,O} coordination, leading to a five-membered chelate ring. Dissociation of the amide protons occurs only for acethydrazide by enolization which allows the formation of a complex with a twice-deprotonated ligand molecule. For the copper(II) systems with oxalodihydrazide and formic hydrazide, the amide groups of the ligands remain protonated, as the appearance of a precipitate at low pH limits further measurements.