Aerobic reaction of a hexadentate redox-active o-aminophenol-based ligand, H4L3 = N,N'-bis(2-hydroxy-3,5-ditert-butylpheny1)-2,2'-diamino(diphenyldithio)-ethane, in CH3OH with Ni-II(O2CCH3)2 center dot 4H(2)O and Et3N afforded isolation of a reddish-brown crystalline solid [Ni(L-3)] 1. Cyclic voltammetry (CV) experiment exhibits two oxidative responses at E-1/2 = 0.09 and 0.53 V vs SCE (saturated calomel electrode). Chemical oxidation of 1 in air by [Fe-III(eta 5-C5H5)(2)][PF6] and AgBF4, in CH,Cl-2 led to the isolation of one-electron oxidized species [1]1 as purple [1][PF6]center dot CH2Cl2 and two-electron oxidized species [1]2 as dark purple [1] [BF4](2)center dot CH2Cl2 respectively. X-ray crystallographic analysis at 100(2) K unambiguously established that the ligand is present in [Ni-II{(L-ON(ISQ))(center dot-)}{(L-S,L-S) (D)-}{(NiLO,NIBQ)-L-II{}(0)center dot}{(L-O,N(ISQ)}]center dot[PF6]center dot[CH2Cl2, and [Ni-II{(L-O,N(IBQ)}(0){(L-O,N(IBQQ))}(0){(L-S,L-S)}][BF4](2)center dot CH2Cl2, as monoanionic o-iminosemiquinonate(1) g-radical (Srad = 1/2) (LISQ center dot-) and neutral o-iminoquinone (1,1139 redox-levels. Complexes 1, [1] [PF6]center dot CH2Cl, and [1][BF4](2)center dot CH2Cl2 possess an S = 2, 3/2, and 1 ground-state, respectively, established by temperature-dependent (2-300 K) magnetic behavior of 1 and [1] [PF6]center dot CH2Cl2, and a yeff value of [1] [BF4](2)center dot CH2Cl2 at 300 K Both 1 and [1] [PF6]center dot CH2Cl2 exhibit ferromagnetic exchange coupling between the two electrons of Nill and two/one ligand 7r-radicals, respectively. The redox processes are shown to be ligand-based. Spectroscopic and redox properties, and density functional theory (DFT) calculations at the CAM-B3LYP-level of theory adequately describe the electronic structure of 1, [1](+), and [1](2+). The observed UV vis NIR absorptions for 1, [1] [PF6]center dot CH2Cl2, and [1] [BF4](2)center dot CH2Cl2 have been assigned, based on time-dependent (TD)-DFT calculations.