Figure 6.

Different model functions B fitting with the results of experiments ($c=5·{10}^{-4}\mathrm{mol}·{\mathrm{L}}^{-1})$. We assumed that different types of gallic acid react with iron(II), which leads to the formation of the following coordination compounds: (a) ${[\mathrm{H}}_4{\mathrm{GAFe}]}^{2+}$, (b) ${[\mathrm{H}}_3{\mathrm{GAFe}]}^{+}$, (c) ${\left[\mathrm{HGAFe}\right]}^{-}$, (d) ${\left[\mathrm{GAFe}\right]}^{2-}$.