Complex formation of silver(I) ion with some aminopolycarboxylate ligands

Abstract

The complex formation of Ag+ with iminodiacetate (IDA), nitrilotriacetate (NTA), 1,2-ethylenediamine-N,N,N′,N′-tetraacetate (EDTA), 1,3-diaminopropane-N,N,N′,N′-tetraacetate (TMTA) and 1,4-diaminobutane-N,N,N′,N′-tetraacetate (TETA) has been studied using potentiometric measurements at 25 °C and I=1(KNO3). The results obtained by different total concentrations of the components in the range 1 × 10−3 to 4 × 10−2 M are interpreted with formation of the following species: (a) IDA: AgHL, AgL− and AgL23−; (b) NTA: AgL2−; (c) EDTA: AgHL2−, AgL3− and Ag2L2−; (d) TMTA: AgHL2−, AgL3−, Ag2L26− and Ag2L2−; (e) TETA: AgHL2−, AgL3−, Ag2L26− and Ag2L2−. In the case of the monoamine ligands the formation of AgL and AgL2, found also for IDA but with K1>K2, is not respected by NTA for which only a 1:1 complex is obtained. The 1:1 complexes with 1,n-alkylenediamine ligands show weak stabilization by further chelation and an increased tendency for dimerization occurs by increasing the number of methylene groups between the two N atoms. EDTA and its homologs form also bimetallic Ag2L2− and protonated AgHL2− complexes in which their stabilities are dominated by the basicities of AgL3− and HL3−, respectively.