Stabilities of 1,2-diethyl-3-hydroxy-4-pyridinone chelates of divalent and trivalent metal ions

Abstract

The stability constants of the 1:1, 2:1 and 3:1 complexes of bidentate 1,2-diethyl-3-hydroxy-4-pyridinone (DEHP) with divalent and trivalent metal ions have been determined by potentiometric and spectrophotometric measurements in KCl supporting electrolyte (0.100 M) at 25.0 °C. The overall log stability constants (β ML3=[ML 3]/[M 3+][L −] 3) for the Fe(III), Ga(III) and In(III) complexes of DEHP are high, 36.75, 36.05 and 32.38, respectively, while that for the relatively weak complex with Gd(III) is 19.76. The crystal structure of the 3:1 indium(III) chelate of DEHP is described. The divalent metal ions, Cu(II), Ni(II), Co(II) and Zn(II), form moderately stable 1:1, 2:1 and 3:1 complexes with DEHP. The thermodynamic stabilities of the Fe(IlI) chelates of DEHP are only moderately greater than those of 1,2-dimethyl-3-hydroxy-4-pyridinone (DMHP, L1). While this difference may suggest a small difference in physiological properties of the two compounds, the main difference in their effectiveness must be due to differences in their behavior in vitro.