Synthesis and characterisation of the mixed-sandwich complex closo-[3-(η-C5Me5)Fe-4-Me2S-1,2-C2B9H10] and its charge-transfer salts; crystal structure of [Fe(η-C5Me5)-(C2B9H10SMe2)]+[ddq]˙–·CH2Cl2(ddq = 2,3-dichloro-5,6-dicyano-p-benzoquinone)

Abstract

The mixed-sandwich ferracarborane complex closo-[3-(η-C₅Me₅)Fe-4-Me₂S-1,2-C₂B₉H₁₀] has been synthesised and characterised by cyclic voltammetry, infrared, ¹H and ¹¹B NMR spectroscopy. This complex forms stable 1 : 1 charge-transfer salts with 2,3-dichloro-5,6-dicyano-p-benzoquinone (ddq) and 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane. Both salts are paramagnetic between 5 and 300 K with Weiss constants of –0.9 and –0.7 K respectively. The organic radical anions do not contribute to the bulk magnetic susceptibilities of these salts. Single-crystal X-ray diffraction analysis of the ddq salt shows that the ddq˙^– anions form isolated stacked dimers within which there is a short interplanar separation of 2.90 Å. Short S ⋯ O contacts (3.15 Å) occur between the [Fe(η-C₅Me₅)(C₂B₉H₁₀SMe₂)]⁺ cations and the quinoidal oxygen atoms of the anions. The room-temperature electrical conductivity of single crystals of the ddq salt is less than 10^–7 S cm^–1.