Synthesis, Structure, and Magnetic Properties of Two {Co₁₆^IICo₄^III} Supertetrahedral T₄ Clusters Formed from the In Situ Dissociation of a Tertiary N-Containing Ligand

Two mixed-valent cobalt clusters {[(CoII)16(CoIII)4(μ6-O)4(μ3-OH)12(OCH3)12(H2O)8(BMBC)4]·(NO3)8} (1) and {[(CoII)16(CoIII)4(μ3-OH)20(OCH2CH3)4(HOCH2CH3)8(BMBC)4]·(NO3)8} (2) were synthesized and constructed by a semiflexible dicarboxylic ligand 4′,4′-[ammoniobis(methylene)]-bis[(1,1′-biphenyl)-2-carboxylate] (BMBC–) with Co(NO3)2·6H2O under solvothermal systems. Interestingly, the ligand BMBC- is afforded from the in situ dissociation reaction of tertiary N-containing organic carboxylic acid ligands. The complexes present a beautiful supertetrahedral T4 cluster formed by an interior Co4IIIO4 cubane and four exterior Co4IIO4 cubanes bridged via μ6-O2 and μ3-OH– ions and stabilized by four BMBC– organic ligands. The complexes were confirmed by single-crystal X-ray diffraction (XRD), elemental analysis, infrared spectroscopy, and thermogravimetric analysis. Furthermore, the magnetic analyses reveal that the [Co20] cluster exhibits an antiferromagnetic behavior.