The reactions of MnIIIEDTA-, MnIIEDTA2-, and Mnill Cy DTA- with superoxide have been studied in both aqueous and nonaqueous solvents. In anhydrous Me2SO, the reduction of MnIIIEDTA- to MnIIEDTA2- by superoxide has been characterized by stopped-flow kinetic measurements, rapid-scan spectrophotometry, electron paramagnetic resonance, and cyclic voltammetry. The reaction is second order with a rate constant of 5*104 M-1 s-1 at 20 °C. The reaction of MnIIICyDTA is analogous, having a rate constant of ~1*106 M-1 s-1. Addition of superoxide to a MnIIEDTA2- solution in Me2SO produces a green intermediate which changes to a yellow-brown final product. Although manganese aminocarboxylate complexes do not catalyze the dismutation of superoxide in aqueous solution, the complexes do react with superoxide. MnIIEDTA- is reduced to MnIIIDTA2-by superoxide in water. MnIIEDTA2- and superoxide interact to form a blue intermediate which dissociates to regenerate MnIIEDTA2- and the spontaneous dismutation products. The reactions of manganese aminocarboxylate complexes with hydrogen peroxide, sodium peroxide, and dioxygen in Me2SO are also discussed. The crystal and molecular structure of KMnEDTA•2H2O has been determined by single-crystal X-ray diffraction techniques by using 1684 unique reflections in the range 2° ≤ 28 ≤ 50°. KMnEDTA-2H2O crystallizes in the orthorhombic space group P21 21 21 with a = 6.579 (1) Å, b = 23.161 (7) Å, and c = 10.054 (3) Å. There are four molecules in the unit cell. Refinement of the nonhydrogen atoms by least-squares procedures gave a final R1 value of 0.065. In the complex anion, the manganese is coordinated by the hexadentate EDTA ligand producing a distorted octahedral MnN2O4 geometry. The closest water molecule is greater than 4 A away from the manganese. The potassium counterion is coordinated to six oxygens from carboxylate and water groups. Average Mn-N and Mn-O (two types) bond lengths are 2.22 (1), 2.03 (1), and 1.90 (1) Å. The presence of two short Mn-O bonds and four long Mn-O and Mn-N bonds is opposite to the distortions observed in the 3d9 CuN2O4 complexes, wherein the metal-oxygen bonds are generally longest, a result thought to be consistent with Jahn-Teller effects. The diffusion coefficients of chemically prepared O2- solutions and of dioxygen in Me2SO have been determined by single-step chronoamperometry. These values, 11 × 10-5 and 2.93 × 10-5 cm2/s, respectively, are in good agreement with less accurate values reported previously by other workers. We also report the electrochemistry of the aforementioned manganese aminocarboxylate complexes. © 1979, American Chemical Society. All rights reserved.
