Experimental data on the charge transfer band position of various carbonato complexes of the general formula [Co(N 4)Co 3] + (N 4(NH 3) 4, (en) 2, (pn) 2, 2, cis[Co(NH 3) 2(Co 3) 2] − and [Co(CO 3) 3] 3− and the vibrational frequencies of carbonyl group as well as the NH stretching frequencies have been obtained. By comparing the ultraviolet band maxima of the carbonato complexes with those of sodium carbonate (purely ionic) and propylene carbonate (purely organic) covalency factors have been evaluated and compared with covalency factors obtained from carbonyl stretching frequencies, which shows a reasonable agreement. Examination of the infrared spectra of both deuterated and undeuterated complexes of [Co(NH 6) 3] 3+, [Co(NH 3) 5(Co 3)] and [Co(NH 3) 4(Co 3] + shows the presence of intramolecular hydrogen bonding between the ammine protons and the oxygen atom of the free end of the carbonate ligand of the type NH…;O in [Co(NH 3) 5(Co 3)] + complex. The covalency factors for the carbonato and oxalato complexes conclusively show that the carbonato complexes are more reactive than the oxalato complexes which is in good agreement with the experimental findings.