Synthesis, Structure, Electrochemistry, and Magnetism of [Mn~(III)Mn~(III)], [Mn~(III)Fe~(III)] and [Fe~(III)Fe~(III)] Cores: Generation of Phenoxyl Radical Containing [Fe~(III)Fe~(III)] Species

摘要

Neutral homo- and heterobinuclear complexes with the general formula [(tmtacn)M_A(salox)_3M_B] where M_A (M_n~(III) or Fe~(III)) is facially coordinated to the cyclic amine 1,4,7-trime-thyl-1,4,7-triazacyclononane (tmtacn) and M_B (M_n~(III) or Fe~(III)) is coordinated to the azomethine nitrogens and phenolate oxygens of the bridging ligand, salicylaldoxime, thus yielding M_AN_3O_3 and M_BN_3O_3 cores. The compounds were characterized by IR, UV/Vis, mass spectrometry, Mossbauer spectroscopy, electrochemistry, and variable-temperature (2-295 K) magnetic susceptibility measurements. The molecular structures of the compounds [(tmtacn)Fe~(III) (salox)_(3-)Fe~(III)] (3) and [(tmtacn)Fe~(III) (tBuSalox)_3Fe~(III)] (4) were established 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 between 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 electrochemistry of all complexes was investigated in detail. For the complexes Fe~(III)Fe~(III) (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.