Electron-transfer salts derived from N,N′-dicyano-p-benzoquinone diimines and the novel dinuclear organometallic donor [Fe2(η-C5Me5)2(µ-SEt)2(CO)2]

Abstract

Reaction of the electron-rich sulfido-bridged complex [Fe₂(η-C₅Me₅)₂(µ-SEt)₂(CO)₂] with electron-acceptor N,N′-dicyano-p-benzoquinone diimines resulted in electron transfer and formation of crystalline 1 : 1 salts of general formula [donor cation][acceptor anion]. The crystal structures of [Fe₂(η-C₅Me₅)₂(η-SEt)₂(CO)₂] and [Fe₂(η-C₅Me₅)₂(µ-SEt)₂(CO)₂][dmdcnqi](dmdcnqi =N,N′-dicyano-2,5-dimethyl-p-benzoquinone diimine) have been determined by X-ray diffraction methods. The neutral donor molecule possesses exact C₂ symmetry, the molecules stacking in linear chains in the crystal with the C₅Me₅ rings of adjacent molecules parallel to each other. The donor cations in the electron-transfer salt also possess exact C₂ symmetry and, moreover, are arranged similarly in the crystal, but with the planar acceptor anions sandwiched between the C₅Me₅ rings and at an angle of 11.4° to these rings. The sequence along the rows is thus one of alternating donor cations (D˙⁺) and acceptor anions (A˙^–), i.e.⋯ D˙⁺A˙^–D˙⁺A˙^–D˙⁺A˙^–⋯. Consistent with the formation of radical cations and anions is a decrease in the Fe ⋯ Fe distance from 3.445(1)Å in the neutral donor molecule to 3.083(2)Å in the donor cation. However, the temperature dependence of the magnetic susceptibility of this salt, when fitted by the Curie–Weiss law, affords a Weiss constant (θ) of only 0.414 K, which suggests that there is little ferromagnetic coupling between the unpaired spins on the radical cations and anions.