Complex Formation Processes of Iron(II), Iron(III), and Cobalt(II) in an Aqueous–Glycinate Medium

The processes of formation of coordination compounds of iron(II), iron(III), and cobalt(II) in aqueous solutions of glycine are studied using the Clark–Nikol’skii oxidation potential method at various temperatures between 288.15 and 318.15 K at ionic strength of the solution (Na(H)ClO4)I = 1.0 mol/L. Experimental curves of the dependence of the EMF system on the concentrations of hydrogen ions, iron(III), iron(II), cobalt(II), and glycine are obtained: pH, pCox, pCred, $${\text{p}}C_{{{\text{Co}}}}^{{2 + }}$$ , and pCGly, respectively. They make it possible to establish that the complexation processes in the studied system proceeds stepwise over a wide pH range from 0.5 to 9.5. Mononuclear coordination compounds of the following composition are formed: [FeHL(H2O)5]3+, [Fe(HL)2(H2O)4]3+, [Fe(HL)(OH)(H2O)4]2+, [CoL(H2O)5]+, [FeL(H2O)5]+, [Fe(HL)2(H2O)4]2+, [Fe(HL)(OH)(H2O)4]+, and [Fe(HL)(OH)2(H2O)3]0, as well as the heteronuclear complex [FeIIICoIIL(H2O)11]4+, [FeIIICoII(L)2(H2O)10]3+. The type and number of coordinated ligands and cations and the general composition of the resulting complex compounds are determined. Chemical models of reactions of complex formation are compiled.