Radial Expansion of 3d Orbitals and the Near Degeneracy of the A41g and E4g Excited States of Octahedral Mn(II) Complexes

Abstract

The relationship between the wavefunctions for mostly 3d3d molecular orbitals and the energies of the nearly degenerate 4A1g4A1g and 4Eg4Eg excited states of octahedral Mn2+ complexes is investigated from two points of view. First, the expressions relating the energy splitting to the degree of covalency have been extended within the framework of the intermediate neglect of differential overlap (INDO) approximation to include the large but previously neglected two‐center Coulomb integrals and all ligand one‐center Coulomb and exchange integrals. The results resemble those previously obtained in their inability to account for the spectral assignment of the 4Eg4Eg state below 4A1g4A1g for the MnF64− complex in the salts KMnF3, RbMnF3, and MnF2. Second, the assumption of identical metal‐ion repulsion integrals for the egeg and t2gt2g molecular orbitals is discarded in a simple analysis of an all‐electron molecular SCF calculation for the MnF64− complex. While both the egeg and t2gt2g orbitals contain a metal‐ion dd orbital that is expanded relative to that for the free Mn2+ ion, the slightly greater radial expansion for the t2gt2g orbital is shown to qualitatively account for the observed ordering of the 4A1g4A1g and 4Eg4Eg states