o-Iminobenzosemiquinonato Complexes of Mn(III) and Mn(IV). Synthesis and Characterization of [MnIII(LISQ)2(LAP)] (S t = 1) and [MnIV(LISQ)2(LAP-H)] (S t = 1/2)

From the reaction of [MnIII 3(μ-O)(μ-CH3CO2)6]CH3CO2 (manganese(III) acetate) and 2-anilino-4,6-di-tert-butylphenol (1:3) in methanol under anaerobic conditions, dark brown-black crystals of [MnIII(LISQ)2(LAP)] (1) were obtained in ∼30% yield. (LAP)- represents the closed-shell o-aminophenolate(−) form of the above ligand, and (LISQ)- is the monoanionic π radical form o-iminobenzosemiquinonate(−) (S rad = 1/2). Complex 1 can be deprotonated at the (LAP)- ligand and one-electron-oxidized by air, yielding crystals of [MnIV(LISQ)2(LAP-H)] (2), where (LAP-H)2- represents the closed-shell, dianionic o-amidophenolate(2−) form of the above ligand. The structures of 1 and 2 have been determined by X-ray crystallography at 100 K. The protonation and oxidation levels of the ligands and of the metal ions have been unequivocally established: both complexes contain two π radical ligands, 1 contains a MnIII ion, and 2 contains a MnIV ion. The spins of the radicals (S rad = 1/2) couple strongly antiferromagnetically with the d4 and d3 configuration of the Mn ions in 1 and 2, respectively, yielding the observed ground states of S = 1 for 1 and S = 1/2 for 2. This has been established by temperature-dependent susceptibility measurements (2−300 K) and S- and X-band EPR spectroscopy.