We recently reported on the synthesis of a new pentadentate N4O ligand, tBuL(-), together with the X-ray diffraction structure of the corresponding mononuclear manganese(HI)-hydroxo complex namely [(tBuL)Mn(III)OH](ClO4), (ClO4)). [El Ghachtouli et al. Energy Environ. Sri. 2011, 4, 2041.] In the present work, we evidence through electrochemical analysis that complex 1(+), in the presence of water, shows a peculiar behavior toward electron-transfer kinetics. The synthesis, single-crystal X-ray diffraction, and EPR spectroscopic characterization of two other mononuclear manganese(III)-chlorido and methoxo complexes-namely, [(tBuL)Mn(III)CIRPF6), (2(PF6)) and [(tBuL)Mn(III)OMe](ClO4), (3(ClO4)) are also reported. 2(PF6) and 3(004) compounds will serve as reference complexes for the electron-transfer kinetics investigation. The peculiar behavior of 1(ClO4) is attributed to the specificity of hydroxide anion as ligand presumably allowing intermolecular hydrogen-bonding interactions and thus affecting electron-transfer properties.