Formal Valence, Charge Distribution, and Chemical Bond in a Compound with a High Oxidation State: KMnO4

Abstract

KMnO4 has unusual formal manganese oxidation state Mn+7 that seems puzzling: the energy of creating such ion (119 eV) is much greater than the energy of chemical bonds (up to ~10 eV). We have used the Wannier functions formalism to analyze the distribution of Mn-3d electrons and O-2p electrons for empty electronic states in the {text{MnO}}_{4}^{ - } complex and have found that, while formally one has {{d}^{0}} configuration for manganese ion in this compound, in reality only about one-half of the hole density described by these Wannier functions corresponding to this configuration belongs to d-electrons, while the other half is spread over surrounding oxygen atoms. This corresponds much more to Mn+7 state than to Mn+2, because the calculated total number of d‑electrons is equal to 5.25. Our analysis has also sown nearly perfect covalent type of chemical bond within the {text{MnO}}_{4}^{ - } complex with negligible contribution of the ionic part.