o-Iminobenzosemiquinonato complexes of Mn(III) and Mn(IV).: Synthesis and characterization of [MnIII(LISQ)2(LAP)] (St=1) and [MnIV(LISQ)2(LAP-H)] (Si=1/2)

From the reaction of [Mn-3(III)(mu-O)(mu-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 [Mn-III(L-ISQ)(2)(L-AP)] (1) were obtained in similar to30% yield. (L-AP)(-) represents the closed-shell o-aminophenolate(-) form of the above ligand, and (L-ISO)(-) is the monoanionic pi radical form o-iminobenzosemiquinonate(-) (S-rad = 1/2). Complex 1 can be deprotonated at the (L-AP)(-) ligand and one-electron-oxidized by air, yielding crystals of [Mn-IV(L-ISO)(2)(L-AP-H)] (2), where (L-AP-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 pi radical ligands, 1 contains a Will ion, and 2 contains a Mn-IV ion. The spins of the radicals (S-rad = 1/2) couple strongly antiferromagnetically with the d(4) and d(3) 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.