Two new mononuclear Fe-II complexes, [(L(5)(2)aH)Fe-II](PF6)(2) (1-(PF6)(2)) and [(L(5)(2)a)Fe-II]BPh4 (2-(BPh4)) have been synthesized with the new aminopyridyl ligand bearing a pivaloylamido arm L(5)(2)aH (2,2-dimethyl-N-[6-({[2-(methyl-pyridin-2-ylmethyl-amino)-ethyl]-pyridin -2-ylmethyl-amino}-methyl)-pyridin-2-yl]-propionamide), or its deprotonated form L(5)(2)a(-). The structures of the ferrous complexes have been determined by X-ray analysis. The mononuclear Fe-II is in a pseudo-octahedral environment in both complexes, the six positions around the metal center being occupied by five nitrogen atoms and one oxygen atom from the ligand. Whatever the protonation state of the amide function, the structures are very similar, the Fe-II being 6-fold coordinated by the two amines, three pyridines, and the oxygen atom from the ligand. These two complexes exhibit an acid/base equilibrium in solution that has been studied by UV-vis spectroscopy and cyclic voltammetry in acetonitrile. The reactivity of 1-(PF6)(2) with H2O2 in methanol affords the formation of a new low-spin Fe-III(OOH) intermediate in which the oxygen atom is retained in the coordination sphere of the metal.