Dimerized p-Semiquinone Radical Anions Stabilized by a Pair of Rare-Earth Metal Ions

Here we report stable p-quinone-radical-bridged rare-earth complexes involving the ligand tetramethylquinone (QMe₄^•-). The complexes, {Y[(QMe₄)^•-Cl₂(THF)₃]}₂ (1) and {Gd[(QMe₄)^•-Cl₂(THF)₃]}₂ (2), where THF = tetrahydrofuran, are sufficiently stable that we can measure the single-crystal structures and perform magnetic and electron paramagnetic resonance measurements. These studies show the presence of a semiquinone form and that the magnetic interaction between the radicals in the dimer is strong and antiferromagnetic.