Five-Coordinate Cobalt(ii) Complexes of Macrocyclic Ligands — A New Reversible Oxygen Carrying System

We report the synthesis and characterization of cobalt(II) complexes with two macrocyclic Schiff base ligands, 5,7,7,12,14,14-hexamethyl-1,4,8,11,-tetraazacyclotetradeca-4,11-diene(Me6 [14]4,11-dieneN4) and 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,14-diene(Me6 [14]4,14-dieneN4), containing a large variety of axial ligands. The complexes are low spin and predominantly five-coordinate, the d–d electronic spectra and electron paramagnetic resonance (epr) spectra being consistent with a square pyramidal ligand environment. The complex [Co(Me6 [14] 4,11-dieneN4)] (ClO4)2 functions as a reversible oxygen carrier in several solvents and in the presence of several Lewis bases. Formation of the oxygen adduct in N, N-dimethylformamide (DMF) has been studied spectrophotometrically and by means of epr.