Synthesis and structure of a charge-compensated ferracarborane, commo-[3,3′-Fe{4-(Me2S)-1,2-C2B9H10}2], and its charge-transfer salt with 2,3-dichloro-5,6-dicyano-p-benzoquinone

The sandwich complex commo-[3,3′-Fe{4-(Me2S)-1,2-C2B9H10}2]1 was synthesised. Its meso and DD/LL isomers are easily separated by fractional recrystallization from acetone and were spectroscopically characterized. The charge-transfer salt [3,3′-Fe{4-(Me2S)-1,2-C2B9H10}2]+[ddq]˙–2 was formed between the DD/LL-1 racemate and 2,3-dichloro-5,6-dicyano-p-benzoquinone (ddq). X-Ray crystallography revealed an increase in the iron-dicarbollide distance on oxidation of DD/LL-1(Fe–C2B3 1.50 A) to the cation in 2(Fe–C2B3 1.54 A). The latter is the first example of a cationic bis(dicarbollyl)metal complex to be crystallographically characterized. The cations and anions pack to form alternating layers in the crystal of 2. Within the [ddq]˙– layer the anions form zigzag chains linked via intermolecular N ⋯ Cl electrostatic interactions (N ⋯ Cl 3.21 A). The cation and anion layers are crossed-linked by weak CH ⋯ O hydrogen bonds between the oxygen atoms of the [ddq]˙– anions and some of the cage CH hydrogen atoms of the cations. Between 5 and 270 K the corrected molar susceptibility of 2 follows the Curie–Weiss law, with a θ value of –2.5 K. The single-crystal electrical conductivity of 2 at room temperature is less than 10 –8 S cm–1.