Asymmetric heterodinuclear FeIIIMII (M = Zn, Cu, Ni, Fe, Mn), CoIIIFeII and FeIIICoII species:: Synthesis, structure, redox behavior, and magnetism

Reactions of an LFeIII unit with an M(PyA)(3)(n-) ion prepared in situ, where L represents 1,4,7-trimethyl-1,4,7-triazacyclononane and PyA(-) is the monoanion of pyridin-2-aldoxime, yield heterodinuclear cations of the general formula [LFeIII(PyA)(3)M](2+), where M = Zn-II (1), Cu-II (2), Ni-II (3), low-spin Fe-II (4) and Mn-II (5). Additionally, we also prepared the diamagnetic species [LCoIII (PyA)(3)Fe-II](2+) (6). The (FeCoII)-Co-III species could not be isolated because a facile intramolecular electron transfer leads to complex 7, [LFeII(PyA)(3)COIII](2+). Compounds 1-7 contain three oximato anions as bridging ligands and are isostructural in the sense that they all contain a terminal metal(III) ion in a distorted octahedral environment (e.g., FeN3O3) and a second six-coordinate metal ion M in a mostly trigonal-prismatic MN6 geometry. Complexes 1-7 were characterized on the basis of elemental analyses, mass spectrometry, IR, UV/Vis, Mossbauer, and EPR spectroscopy, and variable-temperature (2-295 K) magnetic susceptibility measurements. The solid-state structures of 1-7 have also been determined by X-ray crystallography. The cyclic voltammograms of the complexes reveal both ligand-centered and metal-centered redox processes. Analysis of the susceptibility data indicates the presence of antiferromagnetic exchange interactions that decrease in the following order: Fe-III Cu-II (2) > (FeNiII)-Ni-III (3) > (FeMnII)-Mn-III (5), as is expected. We have used X-band EPR spectroscopy of 3 ((FeNiII)-Ni-III) at 2-6 K to establish the electronic ground state in great detail and to complement the magnetic susceptibility measurements. (C) Wiley-VCH Verlag GmbH Co.