The temperature-independent paramagnetism of MnO4−: A coupled Hartree–Fock study

Abstract

Coupled Hartree–Fock calculations of electric and magnetic properties of the isolated closed‐shell permanganate anion show it to be paramagnetic, in agreement with experimental measurements on KMnO₄. Lattice effects on the computed value are small, but the computed paramagnetizability is highly sensitive to changes in the Mn–O bond length, moving from near perfect agreement with the estimated experimental value of ξ ^p=75.9 a.u. for the self‐consistent‐field bond length (R=2.93 a₀) to over twice that value at the experimental distance (R=3.078 a₀). Analysis of the perturbed wave function leads to a physical rationalization of the anomalous sign of the magnetizability: Ligand‐field splitting of the Mn d valence space leads to near‐degenerate occupied and virtual orbitals coupled by induced 2‐center σ↔π rotations. The improvements in magnetic properties that would result from use of a valence complete active space wave function are discussed.