COMPLEXATION OF CIS-Pd(NH3)2Cl2 AND Pd(en)Cl2 WITH 1-AMINOPROPYLIDENE­DIPHOSPHONIC ACID

Abstract

The complexation of cis-Pd(NH3)2Cl2 and Pd(en)Cl2 (en – ethylenediamine) with 1-aminopropylidene-1,1-diphosphonic acid (APrDP, H4L) in solutions with extracellular concentration of chloride ions (0.15 mol/L) at the rations Pd(II):APrDP=1:1, 1:2 and 2:1 has been stu­di­ed by pH-potentiometry, electron and NMR spectroscopy. It has been found that upon interaction in the system cis-Pd(NH3)2Cl2:AprDP=1:1, complexes of the equimolar composition [PdHL(NH3)Cl]2- (lgβ=38.84(4)), [PdHL(NH3)2]- (lgβ=43.14(2)) and [PdL(NH3)2]2- (lgβ=34.91(2)) are formed depending on pH, in which the APrDP molecule is coordinated in a bidentate fashion to the cent­ral ion by the nitrogen atom of the amine group and oxygen atom of the phosphonic group. In the case of twofold excess of ligand, bisligand complexes [PdH4L2]2- (lgβ=59.64(9)), [PdH3L2]3- (lgβ=57.39(19), [PdH2L2]4- (lgβ=52.37(17), [PdHL2]5- (lgβ=44.71(9)) [PdL2]6- (lgβ=36.57(6)) are formed, in which two APrDP molecules are coordinated in a bidentated fashion. At pH>6, complexes [PdHL2(NH3)]5- (lgβ=48.57(6)) and [PdL2(NH3)2]6- (lgβ=42.76(8)) are formed, in which the coordinated phosphonic groups of APrDP are sequentially replaced upon coordination by NH3. molecules. In the systems Pd(en)Cl2:APrDP=1:1 and 1:2, complexes only of equimolar composition: [Pd(en)(H2L)] (lgβ=28.88(9)), [Pd(en)(HL)]- (lgβ=24.67(8)) and [Pd(en)L]2- (lgβ=16.84(9)) are formed, whose coordination sphere contains the nitrogen atom of the amine group and oxygen atom of the phosphonic group of APrDP and two nitrogen atoms of the amine groups of an ethylenediamine. At the ratio Pd(II):APrDP=2:1, the formation of binuclear complexes {[Pd(NH3)2]2L} (lgβ=63.58(22)) and {[Pd(en)]2L} (lgβ= 25.18(4)), in which two palladium atoms have a different coordination environment. The coordination sphere of one of the palladium contains a nitrogen atom of the amine group and an oxygen atom of the phospho­nic group of APrDP, and two NH3 molecules or two amine groups of ethylenediamine. The other palladium coordinates two oxygen atoms of phoshonic groups of APrDP and two NH3 molecules or two amine groups of ethylenediamine.