The effect of the crystal environment on the metal–ligand interaction and the ligand field spectrum of CrF3−6

The octahedral CrF3−6 cluster is studied in two different crystal environments. The available experimental data reveal that the cluster with the largest Cr–F bond distance is at the same time characterized by the largest value of the spectrochemical strength. This paradoxical fact has been shown to be due to the effect of the two different Madelung potentials. In K2NaCrF6, the central Cr ion is situated at a maximum of the Madelung potential; in CrF3, it is situated at a minimum. For the different crystal environments it has also been shown that the increase in covalency, that goes with the introduction of correlation, parallels the covalency that is present already at the Hartree–Fock level.