Different ligands heteropolynuclear ethylenediamine cobalt(II) and nickel(II) in aqueous solution of nitrilotriacetic acid

Coordination equilibria in ternary systems containing cobalt(II) salt, ethylediaminetetraacetic (EDTA) and nitrilotriacetic acid (Nta) were investigated by absorption spectrophotometry at various molar ratios of reagents and at a wide pH- range. Mathematical treatment of obtained data allowed to evaluate the existence of a variety of complex species in solutions and to choose those which were sufficient to describe the experimental results. It was determined the stoichiometry in binary and ternary systems polynuclear Complexones composition (Co(II)-НТА-EDTA) ($2:2:1$, $2:4:1$, $3:6:1$, $4:8:1$), as well as the pH of their existence and stability constants. Also studied hetero polynuclear complexes in the system Co (II)-Ni (II)-НTA-EDTA $1:1:2:1$, $1:2:3:1$ and $2:1:3:1$. Presents the possible structures of the complexes formed. Methods of mathematical modeling by studying the absorption spectra of complex parts, as well as the dependency A = $f$(pH) and A = $f$($\lambda$) revealed the formation of mononuclear complexes of the composition: [CoEdta]$^{2-}$ ($\lg \beta$ = 16.31$\pm$0.06), [CoNta]$^-$ ($\lg \beta$ = 9.86$\pm$0.06), [CoNta$_2$]$^{4-}$ ($\lg \beta$ = 13.56$\pm$0.01), [Co(OH)Nta]$^{2-}$ ($\lg \beta$ = 12.95$\pm$0.01), [CoNtaEdta]$^{5-}$ ($\lg \beta$ = 19.93$\pm$0.04), as well as binuclear Complexes composition: [(CoNta)Edta(NiNta)]$^{6-}$ ($\lg \beta$ = 34.12$\pm$0.01), and tetranuclear [(CoNta)$_2$Edta (NiNta)]$^{7-}$ ($\lg \beta$ = 46.16$\pm$0.13) and [(CoNta)Edta(NiNta)$_2$]$^{7-}$ ($\lg \beta$ = 47.53$\pm$0.05). In assessing the balance properly consider Fisher's criteria. All received constants are valid for a temperature of (20$\pm$2) $^{\circ}$C and the ionic strength of the solution is I $\approx$ 0.2 (NaClO$_4$).