Complex formation of Ni(II) and Fe(III) with the nitrite anion

The stepwise stabilities of the complexes formed by Ni(II) and Fe(III) with the nitrite anion have been determined potentiometrically in an aqueous sodium perchlorate medium of unit ionic strength at 25.0°C. Two fairly weak mononuclear complexes are formed in the Ni(II)-nitrite system with the overall formation constants at β₁ = 5.9±0.9 M^-1 and β₂ = 12±2 M^-2, while for the Fe(III)-nitrite system three mononuclear complexes of moderate strengths, namely β₁ = (3.9±0.7) × 10² M^-1, β₂ = (5±2) × 10³ M^-2 and β₃ = (2.8±0.6) × 10⁵ M^-3, are found. No evidence has been found for the formation of polynuclear or acid complexes in the concentration range studied.