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The electronic spectra of enzyme-model organocobalt(Ⅲ) complexes containing completely or partially conjugated macrocyclic ligands were measured in various solvents to investigate the solvent effect on the charge transfer band for the axial cobalt-carbon bond by the extent of conjugation in the equatorial macrocyclic ring; completely conjugated, CH3CoL, C6H5CoL, CNCoL, CH3CoL', CNCoL', partially conjugated CH3(py)Co(DH)2, CH3CoL', unconjugated dienes, [CH3Co(1,4-CT)](ClO4)2, and open ring, CH3Co(salen). The position of the charge transfer band which corresponds to the cobalt-carbon bond was shifted to a shorter wavelength as the polarity of solvent increased and the transition energy (ET) had a linear relationship with solvent polarity parameter, Z-value, only in the case of completely conjugated system. However, the linear correlation between ET and Z was not observed for partially conjugated and open ring systems.
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