Tetranuclear [Mn_2Co_2], [Mn_2Fe_2], and [Mn_2Mn_2] Complexes with Defective Double-Cubane Cores and Phenoxo and Oxo Bridges: Syntheses, Crystal Structures, and Electronic Properties

摘要

Three new tetranuclear complexes [Mn_2~(III)Co_2~(III)O_2(L)_2]-[ClO_4]_2 (1), [Mn_2~(III)Fe_2~(III)O_2(L)_2][ClO_4]_2 (2), and [Mn_2~(III)Mn_2~(III)-O_2(L)_2][Mn~(II)(NCS)_4] (3) have been synthesized through reactions of the mononuclear [Mn~(III)L] precursor with the corresponding metal perchlorate under aerobic conditions [H_3L = tris(2-salicylaldimine)amine, a condensation product between tris(2-aminoethyl)amine and salicylaldehyde in a 1:3 molar ratio]. These compounds have been characterized by spectroscopic and analytical techniques including singlecrystal X-ray structure analysis, electron paramagnetic resonance (EPR) spectroscopy, M?ssbauer spectroscopy, and magnetic measurements. The structure of 1 consists of oxo-/phenoxo-bridged Co~(III) and Mn~(III) centers in a defective double-cubane topology. The molecules of 2 and 3 have similar structures with the Co~(III) centers changed to Fe~(III) centers in 2 and to Mn~(III) centers in 3. These isostructural complexes have been scrutinized with regard to changes in distortions (distances and angles) of the metal coordination spheres. Magnetic studies indicate that 1, 2, and 3 show predominant antiferromagnetic interactions. Changes in the electronic properties concomitant with changes in the distortions in 1, 2, and 3 are analyzed in terms of magnetostructural correlations.