Abstract
The interaction of K2PdCl4 with ethylenediaminetetra(methylenephosphonic) (edtmp, H8L1) and pentamethylenediaminetetra(methylenephosphonic) (pendtmp, H8L2) acids in solutions with physiological chloride ion concentration (0.15 mol L-1KCl) was studied by pH-potentiometry, UV-Vis and NMR spectroscopy. It was established that in the Pd(II)-edtmp and Pd(II)-pendtmp systems at a metal-ligand ratio of 1:1, complexes of equimolar composition [Pd(H4L1,2)Cl2]4-, [Pd(H3L1,2)Cl]4-, [Pd(H2L1,2)Cl]5-, [Pd(HL1,2)Cl]6-, and [Pd(L1,2)Cl]7- are formed, for which formation constants were calculated, and distribution diagrams of equilibrium concentrations were constructed as a function of solution pH. A bidentate mode of coordination of edtmp and pendtmp to the central metal ion by the nitrogen and oxygen atoms of the phosphonate group in the [Pd(H4L1,2)Cl2]4- complex and a tridentate mode by a nitrogen atom and two oxygen atoms of two phosphonate groups of one aminodi(methylphosphonate) moiety of ligands in complexes of the compositions [Pd(H3L1,2)Cl]4-, [Pd(H2L1,2)Cl]5-,
[Pd(HL1,2)Cl]6-, and [Pd(L1,2)Cl]7- were determined. At the concentration ratio Pd(II)-edtmp=2:1 at pH>3, sparingly soluble hydrolysis products were formed in solutions, indicating the absence of interaction between the non-coordinated aminodi(methylphosphonate) moiety of the ligand and Pd(II) to form a binuclear complex. In contrast to edtmp, the system K2[PdCl4]-pendtmp at a 2:1 ratio exhibited the formation of binuclear complexes [Pd2(H3L2)Cl4]5-, [Pd2(H2L2)Cl2]4-, [Pd2(HL2)Cl2]5-, and [Pd2(L2)Cl2]6-. In the [Pd2(H3L2)Cl4]5- complex, two aminodi(methylphosphonate) moieties of pendtmp are coordinated to two Pd(II) ions in a bidentate mode by nitrogen and oxygen atoms of the phosphonate group, and in the complexes [Pd2(H2L2)Cl2]4-, [Pd2(HL2)Cl2]5-, and [Pd2(L2)Cl2]6-, they are coordinated in a tridentate mode by a nitrogen atom and two oxygen atoms of two phosphonate groups.
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