The complexation between iron(III) ion and glycine in nitrate medium

Summary

In the present work, complex formation between iron(III) ion and glycine was studied by spectrophotometric and enf glass-electrode measurements in a 0.5M NaNO₃ medium, at 25°C. The stability constants of iron(III) hydrolytic species were determined in separate experiments and used in the analysis of the iron(III)-glycine system. The experimental data were explained by the following complexes and formation constants:

$$\begin{gathered} \left[ {FeGly} \right]^{2 + } \log \beta _{1,0,1} = 8.57 \pm 0.01 \hfill \\ \left[ {FeHGly} \right]^{3 + } \log \beta _{1,1,1} = 11.33 \pm 0.02 \hfill \\ \left[ {Fe_2 \left( {OH} \right)_2 Gly} \right]^{2 + } \log \beta _{2, - 2,2} = 12.32 \pm 0.08 \hfill \\ \end{gathered} $$

Stability constants of pure hydrolytic complexes of iron were found to be:

$$\begin{gathered} \left[ {FeOH} \right]^{2 + } \log \beta _{1, - 1,0} = - 2.58 \pm 0.03 \hfill \\ \left[ {Fe\left( {OH} \right)_2 } \right]^ + \log \beta _{1, - 2.0} = - 6.36 \pm 0.05 \hfill \\ \left[ {Fe_2 \left( {OH} \right)_2 } \right]^{4 + } \log \beta _{2, - 2.0} = - 3.15 \pm 0.02 \hfill \\ \end{gathered} $$

Possible structures for the complexes in solution are suggested.