STRUCTURE AND REACTIONS OF AN 8-COORDINATE MN(II) COMPLEX - [MN(TMPA)2](CLO4)2 (TMPA = TRIS[(2-PYRIDYL)METHYL]AMINE)

The synthesis, structure and reaction products of an eight-coordinate Mn(II) complex are described. Tbe reaction of Mn(ClO4)2 . 6H2O with tbe tripodal amine ligand tris(2-methylpyridyl)amine (TMPA) yields the eight-coordinate complex [Mn(TMPA)2](ClO4)2 (1) which crystallizes in the monoclinic space group P2(1)/n with a=9.7063(3), b=10.929(3), c = 18.378(7) angstrom, beta=101.96(3)-degrees. The X-ray structure shows an eight-coordinate Mn(II) ion with coordination to six pyridyl and two amine nitrogens which form a bicapped trigonal antiprism geometry. The oxidation of the Mn(II) complex with H2O2 produces the dioxo-bridged dimeric Mn(III,IV) complex [Mn2(mu-O)2(TMPA)2](ClO4)3 which shows antiferromagnetic coupling between the two valence trapped Mn ions leading to S=1/2 ground state in a 16-line EPR spectrum typical of such dioxo-bridged mixed valent Mn complexes and similar to the EPR spectrum exhibited by the S2 State Photosystem II. While the Mn(II) complex is stable to oxidation by O2, in the presence of catechol in methanol solution, it is readily oxidized by O2 to give the catecholate complex. The oxidation of 3,5-di-t-butylcatechol to the quinone by O2 is catalyzed by 1.