activities of mononuclear copper(II) complexes were studied for the reactions, 1) O2 oxidation of N, N, N′,N′-tetramethyl-1,4-diaminobenzene, and 2) decomposition of hydrogen peroxide. For both reactions, distorted tetrahedral complexes showed much higher reactivities than the complexes of other coordination geometries such as plane, squarepyramid and trigonalbipyramid. This could not be explained in