A study of the magnetic state of O2+ in fluoride salts

Abstract

Static magnetic susceptibility measurements for 4°K < T < 300°K are reported for the following dioxygenyl salts: O₂AsF₆, O₂SbF₆, O₂Sb₂F₁₁, and O₂PtF₆. In contrast to previous studies, we find both spin–orbit coupling and crystal field effects to be important. While the As and Sb compounds are paramagnetic at 4.2°K and have small O₂⁺–O₂⁺ exchange, O₂PtF₆ is ordered at 4.2°K, probably due to O₂⁺–Pt(V) exchange. ESR studies confirm the susceptibility results, except in O₂PtF₆ where a resonance was not detected, and show that the O₂⁺ magnetic state is described by an axial spin Hamiltonian with g_⊥ ∼ 1.98 and g_∥ ∼ 1.74. The ESR linewidth of O₂AsF₆ below 70°K is ∼ 80 G. Above 100°K the linewidth rapidly increases so that above 180°K the line is unobservable. This increase may be due to O₂⁺ motion. NMR shows that the AsF₆ groups in O₂AsF₆ are also rotating above 200°K, probably in some hindered form.