ISO-VALENT AND MIXED-VALENT PHENOXY BRIDGED BINUCLEAR MACROCYCLIC COMPLEXES OF COBALT, IRON AND MANGANESE

The binuclear complexes of a tetraaminodiphenol macrocyclic ligand (H2L) of cobalt(II) and manganese(II) with the composition [M2LX2].H2O (X = Cl or Br) and of iron(II) with the composition [Fe2L(imidazole)2(CH3OH)2](ClO4)2.2CH3OH 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(III)M(II)LCl2Br(CH3OH)]. solvent have been isolated. Variable-temperature magnetic measurements of [Co(III)Co(II)LCl2Br (CH3OH)].0.5CH2Cl2, [Mn2(II)LBr2(CH3OH)2].H2O and [Fe2(II)L(imidazole)2(CH3OH)2] (ClO4)2.2CH3OH 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 anti-ferromagnetic exchange coupling with J = -6.3 and -6.1 cm-1, respectively.