Structure and Magnetism of Cubic Low-Spin 4d5 [RuIII (NH3)6] Br[SO4]

The structure of [Ru(NH3)6]Br[SO4] is reported at ca. 295 K. The space group is cubic Fmm with the ruthenium atom lying at a site of Oh symmetry. There is considerable disorder, particularly involving the sulfate ion, and this implies substantial rotational–translational coupling. The Ru–N bond length is 210.7(7) and the N–H length 100(3) pm. The magnetic susceptibility is reported from 4.5 to 300 K. The ESR spectrum between 105 and 300 K showed a g value of 1.926(5). A simple molecular-orbital model involving the π-covalence parameter kπ,π, spin-orbit coupling for the ruthenium(III) atom and small magnetic exchange completely accounted for the susceptibility and ESR spectroscopic experiments. However, the reduction of kπ,π from unity to 0.94 should be attributed to sources other than π covalence, given further theoretical and experimental evidence.