Proof of Large Positive Zero-Field Splitting in a Ru_2~(5+) Paddlewheel

摘要

We present the synthesis, as well as the structural and magnetic characterization, of [Ru_2(D(3,5-Cl_2Ph)F)_4CI(0.5H_2O)]·C_6H_(14) (D(3,5-Cl_2Ph)F = N,N′-di(3,5-dichlorophenyl)formamidinate), a Ru_2~(5+) compound having a ~4B_(2u) ground state derived from a σ~2π~4δ~2π~(*2)δ~* electron configuration. The persistence of this configuration from 27 to 300 K is shown by the invariance of the Ru-Ru distance. Orientation-dependent magnetic susceptibility (χT) and magnetization (M(H)) data are in accord with a spin quartet ground state with large magnetocrystalline anisotropy associated with a large axial zero-field splitting (D) parameter. Theoretical fits to χT and M(H) plots yielded D/k_B = + 114 K, implying an S = ± 1/2 Kramers doublet ground state at low temperature. Single-crystal and powder EPR data are consistent with this result, as the only observed transition is between the M_s = ± 1/2 Zeeman levels. The g values are g_⊥ = 2.182, g_‖ = 1.970, and D = 79.8 cm~(-1). The totality of the results demands D > > 0.