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

Cis- and trans-isomeric heterotrinuclear-metallic
complexes and their two-electron-oxidation products, cis-/trans-[Cp­(dppe)­Fe­(μ-CN)­Ru­(bpy)2(μ-CN)­Fe­(dppe)­Cp]­[PF6]2 (cis-/trans-1[PF6]2) and cis-/trans-[Cp­(dppe)­Fe­(μ-CN)­Ru­(bpy)2(μ-CN)­Fe­(dppe)­Cp]­[PF6]4 (cis-/trans-1[PF6]4), have been synthesized and structurally characterized.
To the best of our knowledge, the complexes are the first example
of a cis-/trans-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, cis-1[PF6]4 is antiferromagnetic,
and trans-1[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 cis- and trans-14+. Most importantly,
the DFT calculations revealed that the type (antiferromagnetic or
ferromagnetic) and strength (J) of the magnetic interactions
in such compounds can be controlled by the variation (cis or trans) of the diamagnetic central metal configurations.