Zero field splitting, field-dependent magnetization of mixed-valent S = 3/2 Diruthenium(II,III) tetracarboxylates

The 2 K field-dependent magnetization, M(H), of S = 3/2 [RunII/III2(OAc)4]+ was studied. [RuII/III 2(OAc)4]+ exhibits an unusually low magnetization with respect to that predicted by the classical Brillouin function. This reduced value is a consequence of the large anisotropy arising from the large zero-field splitting (ZFS), D (+63 ± 11 cm-1), of the [RuII/III2(OAc)4]+ cation, which alters the energy levels with respect to the isotropic energy levels used to derive the Brillouin function. Analytical expressions for the parallel and perpendicular components of M(H) that include zero-field splitting (ZFS), D, and interdimer coupling, 0, are presented for S=3/2. The expression was derived from second-order perturbation theory for \D\>> gUBH. The experimental data fit very well with g = 2.24 ± 0.01, D = +69.5 cm-1 (D/kB = +100 K), and 0 > 0 > -0.6 K indicative of very weak interdimer interactions for both [RuII/III2(OAc)4]Cl and [RuII/III2(OAc)4]3[CoIII(CN)6].