Interaction between 2-pyrrolidine-1-hydroxymethane-1,1-diphosphonic acid and palladium(II) in aqueous solutions

Abstract

The structure of the 2-pyrrolidine-l-hydroxymethane-l,l-diphosphonic acid (PyrHMDP, H4L) has been determined by X-ray crystallography. Formation of the complexes between K2[PdCl4] and PyrHMDP was studied by pH-potentiometry, UV–Vis spectrophotometry and 31P, 13C and 1H NMR spectroscopy in aqueous solutions containing CKCl = 0.15 mol L−1, which corresponds to the concentration of chloride ions in intercellular fluid. The formation constants were calculated for the protonated forms of the PyrHMDP and for the [PdHLCl2]3− and [PdLCl2]4− complexes. The equilibrium concentration distribution diagram for the complexes of different composition was drawn using the formation constants of the Pd chloro-aqua complexes and the chloride concentration. In equimolar palladium complexes with PyrHMDP the ligand was coordinated in a bidentate manner via the nitrogen atom of the pyrrolidine ring and the oxygen atom of the phosphonic group forming a six-membered chelate ring.