Heteronuclear complexation in the system 1-hydroxyethylidenediphosphonic acid—manganese(ii)—gadolinium(iii) in aqueous solution

Abstract

pH-Potentiometric method in combination with mathematical modeling was used to study the system manganese(ii)—gadolinium(iii)—1-hydroxyethylidenediphosphonic acid (HEDP, H₄L). When both cations simultaneously are present in the solution, the accumulation of heteronuclear forms with the ratio of Gd: Mn: HEDP equal to 1: 1: 1, 1: 1: 2, and 1: 1: 3 was observed already in the strongly acidic pH region, while from homonuclear forms only five complexes were detected in the solution, namely, MnL₂^6–, GdH₄L₂^–, GdH₂L⁺, KGd₂HL₂↓, and K₃Gd₂L₂(OH)↓. It was concluded that heteronuclear complexes are much stronger and replace homonuclear forms in solution.