Novel trinuclear Mn-II/Mn-II/Mn-II complexes - Crystal structures and catalytic properties

Kloskowski M, Pursche D, Hoffmann RD, Pottgen R, Lage M, Hammerschmidt A, Glaser T, Krebs B

Abstract

The trinuclear manganese(II) complexes [Mn-3(L-1)(2)(mu-OAc)(4)]center dot 2Et(2)O {HL1 = (1-hydroxy-4-nitrobenzyl)((2- pyridyl)methyl) ((1-methylimidazol-2-yl)methyl)amine} (1.2EtOH), [Mn-3(L-2)(2)(mu-OAc)(4)] {HL2 = ((1-methylimidazol-2-yl)methyl)(1-hydroxybenzyl)amine (2) and [Mn-3(L-3)(2)(mu-OAc)6] {L-3 = bis(1-methylimidazol-2-yl)methanonel (3) were synthesized. The compounds were characterized by X-ray crystallography, mass spectrometry, IR, UV-vis spectroscopy, and elemental analysis. The manganese atoms in 1 and 2 are bridged by phenol moieties of the ligands and acetates. In 3 they are only bridged by acetates in a mono- and bi-dentate way. The resulting Mn...Mn distances are 3.233(1) angstrom (1), 3.364(1) angstrom (2) and 3.643(7) angstrom (3). In the present compounds different limiting cases for the phenomenon of the carboxylate shift are realized. Besides symmetric mono- and bi-dentate bridging an unusual intermediate is also observed. 1.2EtOH is the first example of a trinuclear model for the OEC that shows catalase activity. Furthermore it was characterized by temperature dependent magnetic susceptibility measurements and a total spin ground state of S-t = 5/2 was found. The results for 1 reveals antiferromagnetic coupling between the central and the terminal manganese ions, with J = 1.2 cm(-1), g = 2.00 (fixed), chi(TIP) = 150 x 10(-6) cm(3) mol(-1).