Molecular and Electronic Structure of Octahedral <i>o</i>-Aminophenolato and <i>o</i>-Iminobenzosemiquinonato Complexes of V(V), Cr(III), Fe(III), and Co(III). Experimental Determination of Oxidation Levels of Ligands and Metal Ions

The coordination chemistry of the ligands 2-anilino-4,6-di-tert-butylphenol, H[LAP], and N,N‘‘‘-bis{2-(4,6-di-tert-butylphenol}diethylenetriamine, H2[(LAP)N(LAP)], 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, [LAP]- and [LAP−H]2-, can be readily oxidized to their o-iminobenzosemiquinonato, [LISQ]-, and o-iminobenzoquinone, [LISB], 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: [CrIII(LISQ)3] (1), [FeIII(LISQ)3] (2), [CoIII(LISQ)3] (3), [VV(LISQ)(LAP−H)2] (4), [VV(LAP−H)2(LAP)] (5), and [VVO{(LAP)N(LAP−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 (Srad = 1/2) couple strongly intramolecularly antiferromagnetically to singly occupied orbitals of the t2g subshell at the respective metal ion but ferromagnetically to each other in 3 containing a CoIII ion with a filled t2g6 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 Mössbauer 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-semiquinonato analogues.