Electronic spectroscopy and ligand-field analysis of cis-carbonato(rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)chromium(III) chloride

Abstract The absorption spectra of microcrystalline salts of cis -[Cr(cyc b )(O 2 CO)] + (cyc b = rac -5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) have been measured between 13,000 and 50,000 cm −1 at temperatures down to 2 K. The vibrational intervals of the electronic ground state were extracted by recording emission and far-IR spectra. The zero-phonon line in the sharp-line absorption spectrum splits into two components by 144 cm −1 . The nine electronic bands due to spin-allowed and spin-forbidden transitions were assigned. Using the observed transitions, a ligand-field analysis has been performed to probe the ligand-field properties of carbonato group in the chromium(III) complex. It is found that the carbonato oxygen has moderately strong σ- and π-donor properties toward chromium(III) ion.