Iso- and mixed-valent phenoxy bridged binuclear macrocyclic complexes of cobalt, iron and manganese

Abstract

The binuclear complexes of a tetraaminodiphenol macrocyclic ligand (H 2L) of cobalt(II) and manganese(II) with the composition [M 2LX 2]βH 2O (X = Cl or Br) and of iron(II) with the composition [Fe 2L(imidazole) 2(CH 3OH) 2](ClO 4) 2·2CH 3OH have been synthesized and spectroscopically characterized. Cyclic voltammetric measurements of the dicobalt(II) complexes have indicated that the generation of Co III-Co II and Co III-Co III species take place quasi-reversibly or irreversibly at about 0.38 and 0.90 V vs SCE, respectively. The dimanganese(II) complexes undergo quasi-reversible one-electron oxidation at about 0.32 V, but further oxidation does not occur up to 1.2 V. The iron(II) complex irreversibly gets oxidized at ca 1 V. The dicobalt(II) and dimanganese(II) complexes can be oxidized with bromine and the mixed-valence complexes [M IIIM IILCl 2Br(CH 3OH)]·solvent have been isolated. Variable-temperature magnetic measurements of [Co IIICo IILCl 2Br (CH 3OH)]·0.5CH 2Cl 2, [Mn 2 IILBr 2(CH 3OH) 2]·H 2O and [Fe 2 IIL(imidazole) 2(CH 3OH) 2] (ClO 4) 2·2CH 3OH have indicated that the mixed-valence cobalt complex behaves as a S = 3 2 system, while both the diiron(II) and dimanganese(II) complexes exhibit antiferromagnetic exchange coupling with J = −6.3 and −6.1 cm −1, respectively.