Synthesis, structural and magnetic characterisation of the electron-transfer salts [Fe2(η-C5Me5)2 (µ-SEt)2(CO)2]2[tcnq] 2 and [Fe2(η-C5Me5)2 (µ-SEt)2(CO)2][tcne] (tcnq = 7,7,8,8-tetracyanoquinodimethane; tcne = tetracyanoethylene)

Abstract

Reaction of the electron-rich thiolate-bridged complex [Fe ₂ (η-C ₅ Me ₅ ) ₂ (µ- SEt) ₂ (CO) ₂ ] with 1 molar equivalent of the electron-acceptor compounds 7,7,8,8-tetracyanoquinodimethane (tcnq) and tetracyanoethylene (tcne) is accompanied by electron transfer and resulted in the formation of the dark green crystalline salts [Fe ₂ (η-C ₅ Me ₅ ) ₂ (µ- SEt) ₂ (CO) ₂ ] ₂ [tcnq] ₂ 1 and [Fe ₂ (η-C ₅ Me ₅ ) ₂ (µ- SEt) ₂ (CO) ₂ ][tcne] 2 respectively. The crystal structures of these salts have been determined by X-ray diffraction methods and the cations thereof established to have very similar stereochemistries. The C ₅ Me ₅ ligands are cis disposed with respect to the Fe · · · Fe vector with the dihedral angles between their planes being 71 and 68° for 1 and 2 respectively. The Fe · · · Fe distances are respectively 3.077(2) and 3.069(2) Å. Crystals of 1 consist of isolated units of composition D ^˙+ (A) ₂ ^2- D ^˙ where D ^˙+ denotes the cation and (A) ₂ ^2- a (tcnq) ₂ ^2- dimer, the planes of the tcnq moieties comprising the dimer and those of the adjacent C ₅ Me ₅ rings being virtually parallel. The compound is paramagnetic. Crystals of 2 consist of parallel rows of cations and tcne ^˙- anions in the sequence · · · D ^˙ A _A ^˙- D ^˙+ A _B ^˙- D ^˙+ A _A ^˙- D ^˙+ A _B ^{˙ -} · · ·, where A _A ^˙- and A _B ^˙- label crystallographically independent anions. The two types of tcne ^˙- anion are themselves approximately planar, but define different angles to the planes of the adjacent C ₅ Me ₅ rings of 4 and 72°. Magnetic susceptibility measurements for 2, in the range 5.0 to 310.0 K, suggest very little magnetic coupling between the unpaired spins on the cations and the tcne ^˙- anions and thus this compound is also paramagnetic.