Table 5. Ionic Radii and Midpoint Potentials of 3+/2+ Couples of Analogous Complexes of Fe and Mn^a.

property/metal	Mn	Fe
ionic radius of 3+ state (pm)	78.5 pm	78.5 pm
ionic radius of 2+ state (pm)	97 pm	92 pm
E°′ of (H2O)6 complexb	1.51 V	0.77 V
E°′ of EDTA complexc	0.83 V	0.10 V
E° of LM(H2O)(OH–), M = Mn, Fe	0.42 V	0.05 V
L = 2,6-diacetylpyridinebis(semioxamazide) = dapsox, at pH 7.8d
E° of LM(OH–), M = Mn, Fe	–1.51 V	–1.79 V
L = N[CH2CH2NC(O)NHC(CH3)3]3 (in DMSO vs Fc+/0)e
E° of (Fe)SOD at pH 7.4f,g	>0.9	0.1
(Mn)SOD at pH 7.8g,h	0.3	–0.25

^aAll midpoint potentials are in water and reported vs NHE unless stated otherwise.

^bReference (171).

^cReference (172).

^dReference (173).

^eReference (174).

^fReference (74a).

^gBecause of the slow equilibration of SOD with mediators, on the order of hours, the titrations should be considered to be in quasi-equilibrium only, and the obtained midpoint potentials are therefore only ± ∼50 mV.^74a,131,175

^hReference (75a).