An experimental (120 K) and theoretical electron density study of KMnO4 and KClO4

The experimental electron density _(r) of the two isomorphic salts KMnO4 and KClO4 was determined by a multipole analysis of accurate X-ray diffraction data at 120 K. The quantum theory of atoms in molecules was applied to _(r) and to its Laplacian r2_(r). The bonds were characterized using the topological parameters at the bond critical points of the density _(r), r2_(r), G(r) (kinetic energy density), V(r) (potential energy density) and H(r) (total energy density). According to the classi®cation recently proposed by Espinosa, Alkorta, Elguero & Molins [J. Chem. Phys. (2002), 117, 5529±5542], the KÐO and ClÐO bonds have a pure ionic and covalent character, respectively, while the MnÐO bonds show an intermediate behaviour. The results of the topological analysis of the experimental and theoretical (fully periodic Hartree±Fock and density functional calculations) electron density are in good agreement, even on a quantitative level. The atomic charges, determined by performing an integration over the topological basins, are about +2 e for Mn and Cl atoms. The ionic radius, estimated with the distance of the bond critical point from the nucleus, is in agreement with a charge of +2 e for the Mn atom.