From Antiferromagnetic to Ferromagnetic Interaction in Cyanido-Bridged Fe(III)–Ru(II)–Fe(III) Complexes by Change of the Central Diamagnetic Cyanido-Metal Geometry

<i>Cis</i>- and <i>trans</i>-isomeric heterotrinuclear-metallic complexes and their two-electron-oxidation products, <i>cis</i>-/<i>trans</i>-[Cp­(dppe)­Fe­(μ-CN)­Ru­(bpy)₂(μ-CN)­Fe­(dppe)­Cp]­[PF₆]₂ (<i>cis</i>-/<i>trans</i>-<b>1</b>[PF₆]₂) and <i>cis</i>-/<i>trans</i>-[Cp­(dppe)­Fe­(μ-CN)­Ru­(bpy)₂(μ-CN)­Fe­(dppe)­Cp]­[PF₆]₄ (<i>cis</i>-/<i>trans</i>-<b>1</b>[PF₆]₄), have been synthesized and structurally characterized. To the best of our knowledge, the complexes are the first example of a <i>cis</i>-/<i>trans</i>-isomer with multistates. Although separated by the diamagnetic cyanido-metal bridge, the two distant paramagnetic metal centers in both the oxidized complexes exhibit quite strong magnetic couplings. As a unique example, <i>cis</i>-<b>1</b>[PF₆]₄ is antiferromagnetic, and <i>trans</i>-<b>1</b>[PF₆]₄ is ferromagnetic. Density functional theory (DFT) calculations suggest that the spin-delocalization mechanism should be responsible for the magnetic interactions between the two distant paramagnetic Fe­(III) centers across the diamagnetic cyanido-metal in both <i>cis</i>- and <i>trans</i>-<b>1</b>⁴⁺. Most importantly, the DFT calculations revealed that the type (antiferromagnetic or ferromagnetic) and strength (<i>J</i>) of the magnetic interactions in such compounds can be controlled by the variation (<i>cis</i> or <i>trans</i>) of the diamagnetic central metal configurations