Three transition metal complexes formed wiht tripodal polyimidazole ligands: synthesis, crystal structues and reactivity toward superoxide

摘要

Two new tripodal heptadentate ligands, tris{2-[2-(I-methyl)imidazolyl]methyliminoethyl}amine ?mim)3tren) and tris{2-[2-(I- methyl)imidazolyl]methylaminoethyl}amine ?mim)3htren), containing polyimidazole groups were synthesized. Three correspond- ing metal complexes [Fe(mim)_3tren](PF_6)_2 (I) [Mn(mim)_3tren](CIO_4)_2.MeCN (2) and [Mn(mim)_3htren](CIO_4)_2 (3) were prepared and characterized by X-ray crystallography. The metal atoms in I and 2, being in distorted [MN6] octahedra, are coordinated by the three imine nitrogen atoms and the three imidazole nitrogen atoms with M-N bond distances of 2.180(4)-2.260(4) and 2.268(3)-2.312(3) A for I and 2, respectively. In 3, the Mn(II) atom is hepta-coordinated by seven nitrogen atoms from htren(mim)3 to form a mon9capped,anti-trigonal prism with the Mn-N_(imine), Mn-N_(imine) and Mn-N_(tripodal) bonds having lengths of 2.235(7), 2.369(6) and 2.507(10) A, respectively. The reactivities of the complexes with superoxide have been investigated by UV-Vis and electrochemical methods, showing that a new species symbolized as a [Fe-O_2("-) or [Mn-O_2~("-) adduct was formed and that these complexes are effective superoxide scavengers.