Magnetic Properties and Optical Absorption Spectrum of K2ReCl6

Abstract

A phenomenological theory of certain physical properties of the (ReCl₆)²⁻ complex ion is presented here. The ion can be described in terms of a set of parameters which includes the strength of the octahedral ligand field, the Coulomb integrals, the spin‐orbit coupling constant and the orbital reduction factors. The interaction matrices for the three‐electron system are given in algebraic form. With an appropriate choice of the parameters the eigenvalues of these matrices are in fair agreement with the observed energy levels of the system. The effect of a departure from strict octahedral symmetry is discussed. The matrix elements of the magnetic moment operator are also given in algebraic form and then used in a calculation of the susceptibility. The discrepancy between theory and experiment is attributed to a superexchange interaction which leads, at sufficiently low temperatures, to antiferromagnetism of the compound. Finally, the results of paramagnetic resonance experiments on K₂ReCl₆ are considered.