AXIAL COORDINATION IN COBALT(II) COMPLEXES OF TWO SYNTHETIC MACROCYCLIC LIGANDS CONTAINING THE BIDENTATE α-DIIMINE GROUP

Abstract

In order to elucidate the nature of axial coordination in synthetic macrocyclic complexes of cobalt(II), we have synthesized two new series of such complexes, containing the macrocycles Me₄ [14] 1,3,8,10-tetraeneN₄ and Me₂ [14] 1,3-dieneN₄, by direct isolation of the Co(II) complexes from the condensation reaction mixtures. The complexes are formally five-coordinate in the solid state, but exhibit a tendency toward six-coordination in the presence of potential axial ligands, as demonstrated by electronic spectral and electron paramagnetic resonance studies. The Co(tetraeneN₄)⁺² and Co(dieneN₄)⁺² species are compared with the previously studied Co(Me₆ [14] 4, 11-dieneN₄)⁺² moiety with respect to axial coordination. It is concluded that the presence of methyl substituents on the six-membered chelate rings of the latter complex have a marked effect on its tendency to coordinate axial ligands.