Coordination properties of some nickel(II) monophosphono dipeptides species in aqueous solution: The role of phosphonic oxygen in complex stabilization and ligand-fields analysis

Abstract

Equilibrium studies on the nickel(II) complexes of oxygen and nitrogen donor ligand (monophosphono dipeptides: 1- ( N- l-leucylamino)methylphosphonic acid – Leu-Gly(P), and a thioether sulfur donor ligands (monophosphono dipeptides: 1- N-(glycyloamino)-2-( S-benzylthio)ethanephosphonic acid – Gly-(Bz)Cys(P), d(−) and Gly-(Bz)Cys(P), d(+) were performed by potentiometric titration and NIR–Vis spectroscopy. Additionally, the ligand-field parameters (CFM/AOM) were estimated and discussed in the tetragonal distortion framework. The lowest tetragonal distortion was observed in the case of the [NiHL] species, whereas the strongest in the case of [NiL 2] species. In the latter species the ligand-field analysis confirms the coordination of the deprotonated phosphonic groups to the metal ions in both axial positions. In the case of nickel(II) complexes with Gly-(Bz)Cys(P), d(−) or Gly-(Bz)Cys(P), d(+) additional interaction between sulfur donor atom and nickel(II) was suggested.