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 sys-tem. 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.
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