Electron paramagnetic resonance and UV–Vis absorption study of trans-(1,4,8,11-tetraazacyclotetradecane)chromium(III) complexes

The electronic structures of the trans-[CrIII(cyclam)X2]n+ (cyclam=1,4,8,11-tetraazacyclotetradecane, X=Cl−, OH−, and H2O) were investigated. The spin quartet excited states of these complexes were assigned on the basis of a Gaussian analysis of UV–Vis absorption spectra. The spin Hamiltonian parameters of the ground states, especially the zero-field splittings, were determined from the randomly oriented frozen solution electron paramagnetic resonance spectra. The calculated zero-field splitting parameters determined from the second-order spin–orbit couplings with the nearest excited quartet states were found to deviate from those observed experimentally. The deviations were found to reflect the bond covalency of the axial ligators.