Covalency effects in the spectrum of the tetrachloroferrate(III) anion

The ligand field approach to the interpretation of the visible spectrum of the tetrachloroferrate(III) anion has been critically reviewed. The influence of differences in the delocalisation of the metal t2 and e orbitals has been considered. This covalency influence could be worked out either by using different nephelauxetic parameters or by introducing different crystal field parameters. Both approaches were found to give a satisfactory explanation of the relative positions and the number of bands in the spectrum, although the agreement between calculated and observed energies is not very good.