The coordination chemistry of the ligands 2-anilino-4,6-di-tert-butylphenol, H[L-AP], and NY " ' -bis{2-(4,6-di-tert-butylphenol}diethylenetriamine, H-2[(L-AP)N(L-AP)], has been studied with the first-row transition metal ions V, Cr, Fe, and Co. The ligands are noninnocent in the sense that the aminophenolato parts, [L-AP](-) and [L-AP-H](2-), can be readily oxidized to their o-iminobenzosemiquinonato, [L-ISQ](-), and o-iminobenzoquinone, [L-ISB], forms. The following neutral octahedral complexes have been isolated as crystalline materials, and their crystal structures have been determined by X-ray crystallography at 100 K: [Cr-III(L-ISQ)(3)] (1), [Fe-III(L-ISQ)(3)] (2), [Co-III-H(L-ISQ)(3)] (3), [V-V(L-ISQ)(L-AP-H)(2)] (4), [V-V(L-AP-H)(2)(L-AP)] (5), and [(VO)-O-V{(L-AP)N(L-AP-H)}} (6). From variable-temperature magnetic susceptibility measurements and X-band EPR spectroscopy it has been established that they possess the ground states: 1, S = 0; 2, S = 1; 3, S = 3/2; 4,S = 1/2; 5, S = 0; 6, S = 0. The o-iminobenzosemiquinonato radicals (S-rad = 1/2) couple strongly intramolecularly antiferromagnetically to singly occupied orbitals of the t(2g) subshell at the respective metal ion but ferromagnetic ally to each other in, 3-containing 6 a Co-III ion with a filled t(2g)(6) subshell. It is demonstrated that the oxidation level of the ligands and,metal ions can be unequivocally determined by high-quality X-ray crystallography in conjunction with EPR, UV, vis, and Mossbauer spectroscopies. The spectro- and electrochemistry of these complexes have also been studied in detail. Metal- and ligand-based redox chemistry has been observed. The molecular and electronic structures are compared with those of their o-semiquimonato analogues.