Electron paramagnetic resonance study of dichlorodioxomanganese(VI), MnO2Cl2

Abstract

X-Band e.p.r. spectra of magnetically dilute solutions of MnO₂Cl₂ in CCl₄ have been recorded at 77 K and at 298 K and are analysed in detail. The spin–orbit coupling constants, ξ_Mn and ξ_Cl, at the manganese and chlorine atoms in this compound are estimated to be 248 and 587 cm^–1 respectively. At 77 K, MnO₂Cl₂ rotates about its X-axis in CCl₄ solution. Spin-Hamiltonian parameters are listed for 298 K, for 77 K, and for the rigid molecule, and are equated to the atomic orbital coefficients in the molecular orbitals involved in bonding in this molecule. The unpaired electron lies in the metal ion 3d_x²–y² orbital mixed with a small amount (8%) of the 3d_z² orbital, and it is strongly (55%) delocalised on to the ligands. Two of the principal components of the g-tensor are larger than the spin-only value, a situation unusual in d¹ complexes. This is shown to be due to relatively large spin–orbit coupling at the chlorine atoms. It is pointed out that principal values of the g-tensor may be used to distinguish distorted tetrahedral complexes which are stretched along their z-axes from the corresponding complexes compressed in this direction, provided that spin–orbit interactions at the ligands are relatively large.