INTERACTION OF CIS-Pd(NH3)2Cl2 WITH DIPHOSPHONIC ACIDS IN SOLUTIONS AT PHYSIOLOGICAL CHLORIDE-IONS CONCENTRATION

Abstract

The complex formation of cis-Pd(NH3)2Cl2 with 1-hydroxyethylidene-1,1-diphosphonic (HEDP, H4L1), 3-amino-1-hydroxypropylidene-1,1-diphosphonic (AHPrDP, H4L2), and 1-aminopropylidene-1,1-diphosphonic (APrDP, H4L3) acids in aqueous solutions with the concentration CKCl=0.15 mol/L, which corresponds to the concentration of chloride ions in the intercellular fluid, has been studied by spectrophotometry and pH potentiometry. The results of studying the interaction between cis-Pd(NH3)2Cl2 and diphosphonic acids have been interpreted taking into account the equilibrium concentration distribution of complexes forming in Pd(NH3)2Cl2 solutions at a chloride ion concentration of 0.15 mol/L. It has been found that when Pd(NH3)2Cl2 is dissolved in 0.15 mol/L KCl, ammonia molecules are substituted by chloride ions and a water molecule in the pH range of 2 – 4 to form chloro-aqua complexes [PdCl4]2- and [PdCl3(H2O)]-.
 In the case of complex formation of Pd(II) chloro-aqua complexes with HEDP and AHPrDP, complexes with [Pd 2OPO3 2Cl] chromophore with bidentate coordination of ligands by two oxygen atoms of phosphonic groups are formed in the acidic pH range. At pH>5, a [Pd(L1)(NH3)2]2- complex (lgβ=30.55(5)) is formed in the cis-Pd(NH3)2Cl2:HEDP=1:1 system, and at pH>6, a [Pd(HL2)(NH3)2]- complex (lgβ=40.29(2)) is formed in the cis-Pd(NH3)2Cl2:AHPrDP=1:1 system. The formation of complexes with [Pd 2OPO3 2Namine] chromophore takes place with the displacement of chloride ions from the coordination sphere of complexes with [Pd 2OPO3 2Cl] chromophore by ammonia molecules.
 In the system cis-Pd(NH3)2Cl2:APrDP=1:1, the ligand is coordinated to Pd(II) in a bidentate fashion by the nitrogen atoms of the amine group and oxygen atoms of the phosphonic group to form a [Pd(H2L3)Cl2]2- complex with [Pd Namine OPO3 2Cl] chromophore in the acidic pH range. When pH is increased to 5 and then to 7, a sequential substitution of chloride ions by ammonia molecules takes place to form a [Pd(HL3)(NH3)Cl]2- complex (lgβ=38,84(4)) with [Pd 2Namine OPO3 Cl] chromophore and a [Pd(HL3)(NH3)2]- complex (lgβ=43,14(2)) and [Pd(L3)(NH3)2]2- complex (lgβ=34.91(2)) with [Pd 3Namine OPO3] chromophore.