Influence of the central diamagnetic cyanidometal on the distant magnetic interaction in cyanide-bridged Fe(III)-M(II)-Fe(III) complexes.

Abstract

To investigate how the central diamagnetic cyanidometal influences the distant magnetic interaction of cyanide-bridged Fe(III)-M(II)-Fe(III) complexes, cis-[Cp(dppe)Fe(II)(NC)M(II)(L)2(CN)Fe(II)(dppe) Cp][PF6]2 (M = Os, L = bpy 1; M = Os, L = phen 2; M = Fe, L = bpy 3; M = Fe, L = phen 4), and their one-electron oxidation products 5–7 and two-electron oxidation products 8–11 were synthesized and fully characterized. The cyclic voltammetry of complexes 1–4 suggests that both NC-Os(II)(L)2-CN and NC-Fe(II)(L)2-CN have electronic communication ability. The electronic absorption spectroscopy suggests the presence of the central M(II) to the terminal Fe(III) and the terminal Fe(II) to the terminal Fe(III) metal to metal charge transfers (MMCTs) in 5-7 and the central M(II) to the terminal Fe(III) MMCTs in 8-11. Moreover, for the two-electron oxidation products the MMCT energy increases with the central metal in the order Fe < Os < Ru. The two-electron oxidation complexes 8 and 9 exhibit a strong antiferromagnetic coupling (J ≈ -26 cm(-1)) between the two distant Fe(III) ions although separated by the diamagnetic cyanidometal NC-Os(II)(L)2-CN bridge. To the best of our knowledge, this is the strongest magnetic coupling between the distant paramagnetic metal ions across a diamagnetic cyanidometal bridge reported by far. For the two-electron oxidation complexes 10 and 11 with the diamagnetic NC-Fe(II)(L)2-CN bridge, however, the distant two Fe(III) ions possess only very weak antiferromagnetic coupling (J = -0.15 and -0.19 cm(-1)). Combined with our previous reported results, it could be found that the magnetic coupling strength between the distant Fe(III) ions increases with the diamagnetic cyanidometal bridge in the order of Fe < Ru < Os.