Inorganic Chemistry, Vol.44, No.13, 4485-4498, 2005
Synthesis, characterization, and physicochernical properties of manganese(III) and manganese(V)-oxo corrolazines
The structural and physicochemical properties of the manganese-corrolazine (Cz) complexes (TBP(8)Cz)Mn-V&3bond; O (1) and (TBP(8)CZ)Mn-III (2) (TBP = p-tert-butylphenyl) have been determined. Recrystallization of 2 from toluene/ MeOH resulted in the crystal structure of (TBP(8)Cz)Mn-III(CH3OH) (2(.)MeOH). The packing diagram of 2(.)MeOH reveals hydrogen bonds between MeOH axial ligands and meso N atoms of adjacent molecules. Solution binding studies of 2 with different axial ligands (CI-, Et3PO, and Ph3PO) reveal strong binding, corroborating the preference of the Mn-III ion for a five-coordinate environment. High-frequency and field electron paramagnetic resonance (HFEPR) spectroscopy of solid 2(.)MeOH shows that 2-MeOH is best described as a high-spin (S = 2) Mn-III complex with zero-field splitting parameters typical of corroles. Structural information on 1 was obtained through an X-ray absorption near-edge structure (XANES)/extended X-ray absorption fine structure (EXAFS) study and compared to XANES/ EXAFS data for 2-MeOH. The XANES data for 1 shows an intense pre-edge transition characteristic of a high-valent metal-oxo species, and a best fit of the EXAFS data gives a short Mn-O bond distance of 1.56 angstrom, confirming the structure of the metal-oxo unit in 1. Detailed spectroelectrochemical studies of 1 and 2 were performed revealing multiple reversible redox processes for both complexes, including a relatively low potential for the Mn-v -> Mn-IV process in 1 (near 0.0 V vs saturated calomel reference electrode). Chemical reduction of 1 results in the formation of a (MnMnIV)-Mn-III(mu-O) dimer as characterized by electron paramagnetic resonance spectroscopy.