Binuclear Co(II)Co(II), Co(II)Co(III) and Co(III)Co(III) complexes are reported of dianionic ligands, L2−, derived from the condensation of two mol of salicylaldehyde, or substituted salicylaldehydes, and one mol of methanediamine or phenyl substituted methanediamines. Direct evidence for the binuclear nature of the compounds is provided by X-ray structural and FAB mass spectroscopy data. Oxidation of the Co(II)Co(II) complexes, [Co2L2], with iodine, in the presence of pyridine, produces two types of compounds depending on the nature of L: mixed valence Co(II)Co(III) dimers of [Co2L2(py)2](I3) stoichiometry, in the case of the phenylmethane derivatives and fully oxidised Co(III)Co(III) dimers, [Co2L2(py)4](I3)2,
obtained from the complexes with methanediamine. The crystal structures of [Co2(salben)2(py)2](I3) and [Co2(salmen)2(py)4](I3)2 (salben =
N,N′-phenylmethanediyldiphenato, salmen =
N,N′-methanediyldiphenato) have been determined. In both dimers the Co atoms are bridged by two bis-bidentate ligands. The coordination geometry of the Co(II) chromophore, CoN2O2, was found to be distorted tetrahedral, as preliminarily suggested by near infrared and room-temperature magnetic susceptibility data. The Co(III) environments, CoO2N4, involving two additional pyridine nitrogens, are regular octahedral. The magnetic behaviour of representative compounds has been determined and discussed.