Synthesis,structure,electrochemistry,and magnetismof[Mn~(III)Mn~(III)],[Mn~(III)Fe~(III)]and [Fe~(III)Fe~(III)]cores:generation of phenoxyl radicalcontaining [Fe~(III)Fe~(III)]Species

摘要

Neutral homo- and heterobinuclear complexes with the gen-eral formula [(tmtacn)M_A(salox)_3M_B] where M_A (Mn~(III) or Fe~(III)) is facially coordinated to the cyclic amine 1,4,7-trime-thyl-1,4,7-triazacyclononane (tmtacn) and M_B (Mn(III) or Fe~(III)) is coordinated to the azomethine nitrogens and phenolate oxygens of the bridging ligand, sahcylaldoxime, thus yielding M_AN_3O_3 and M_BN_3O_3 cores. The compounds were characterized by IR, UV/Vis, mass spectrometry, Mdssbauer spectroscopy, electrochemistry, and variable -temperature (2-295 K) magnetic susceptibility measurements. The mo-lecular structures of the compounds [(tmtacn) Fe~(III)(salox)3 Fe(III)] (3) and [(tmtacn)Fe”’(tBuSalox)_3Fe~(III) (4) were estab-lished by X-ray diffraction. Three oximate groups -HC=N-O bridge the metal centers with Fe···Fe separations of 3.571(1) and 3.486(1) A for (3) and (4), respectively. Analysis of the susceptibility data yields antiferromagnetic interactions be-tween the metal centers for the complexes Fe~(III)Fe~(III) and Mn~(III)-Fe~(III), but a ferromagnetic interaction for Mn~(III)Mn~(III). The elec-trochemistry of all complexes was investigated in detail. For the complexes Fe”’Fe”’ (3) and (4) a series of reversible one-electron transfer waves leads to the formation of the cations [Fe_2]~(1+/2+/3+) that are attributed to the generation of salox-based phenoxyl radicals.