Electronic Spectroscopy and Ligand Field Analysis of cis-(Cr(cycb)Cl 2 )Cl

The sharp-line absorption spectrum of microcrystalline samples of cis-[Cr(cycb)Cl2]Cl (cycb = rac-5,5,7,12,12,14hexamethyl-1,4,8,11-tetraazacyclotetradecane) has been measured between 13000 and 16000 cm at temperatures down to 5K. The 77K emission and excitation spectra, and 298 K infrared and visible absorption spectra have also been measured. 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 coordinated atoms in the title chromium(III) complex. The zero-phonon line in the sharp-line absorption spectrum splits into two components by 240 cm, and the large Eg splitting can be reproduced by the modern ligand field theory. It is confirmed that nitrogen atoms of the macrocyclic cycb ligand have a strong σ-donor character, but chloride ligand has weak σand π-donor properties toward chromium(III) ion.