$6\mathrm{.}8$ The following Table lists stability constants for a range of substituted tris$-(1,10-$

phenanthroline$)$iron$($II$)$ complexes $),$ together with the $p{K}_a$ values of the

respective ligands, some Hammett $$ values for substituents, and redox potentials

$({}^0)$ for the respective iron$($II$)/$iron$($III$)$ complex couples. Construct graphs

showing the relations between the given stability constants and the other

parameters, and comment on the correlations $($or non$-$correlations$)$ which become

apparent.

The stability constant for the formation of tris$-(1,10-$phenanthroline$)$iron$($III$)$ is

${10}^{14}($i$.$e$.log{}_3=14).$ Why is this value smaller than that for the analogous

iron$($II$)$ complex?