Cobalt(III) Bis-o-semiquinone Complexes with p-Tolyl-Substituted Formazan Ligands: Synthesis, Structure, and Magnetic Properties

Abstract—New heteroligand cobalt(III) bis-3,6-di-tert-butyl-o-benzosemiquinone complexes with p-tolyl-substituted formazan ligands Co(3,6-SQ)₂Lⁿ (L¹H is 1,5-diphenyl-3-p-tolylformazan (I), L²H is 1,3,5-tri-p-tolylformazan (II), and L³H is 3-nitro-1,5-di-p-tolylformazan (III)) are synthesized and characterized. The molecular structures of compounds I, II, and III in the crystalline state are determined by X-ray diffraction (XRD) (CIF files CCDC nos. 2161722 (I), 2167094 (II), and 2167095 (III)). According to the XRD results and magnetic and spectral measurement data, compounds I–III are complexes of low-spin cobalt(III) bound to two radical anion o-semiquinone ligands and one formazan anion. The magnetic behavior of the complexes in a temperature range of 2–300 K is characterized by intramolecular antiferromagnetic exchange interactions between the o-semiquinone ligands. The replacement of the phenyl substituents by p-tolyl groups in positions 1 and 5 of the diamagnetic formazanate ligand results in a significant enhancement of the exchange between the radical centers.