Tetranuclear [Mn₂Co₂], [Mn₂Fe ₂], and [Mn₂Mn₂] complexes with defective double-cubane cores and phenoxo and oxo bridges: Syntheses, crystal structures, and electronic properties

Three new tetranuclear complexes [Mn^III₂Co ^III₂O₂(L)₂][ClO₄] ₂ (1), [Mn^III₂Fe^III ₂O₂(L)₂][ClO₄]₂ (2), and [Mn^III₂Mn^III₂O₂(L) ₂][Mn^II(NCS)₄] (3) have been synthesized through reactions of the mononuclear [Mn^IIIL] precursor with the corresponding metal perchlorate under aerobic conditions [H₃L = 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 single-crystal X-ray structure analysis, electron paramagnetic resonance (EPR) spectroscopy, Mössbauer 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.