Crystal and molecular structure of tetramethylammonium carbidohexadecacarbonylhexaferrate(2–), [Me 4 N] 2 [Fe 6 (CO) 16 C], a hexanuclear iron cluster complex with an encapsulated six-co-ordinate carbon atom

The title compound crystallizes in the centrosymmetric orthorhombic space group Pnma, with a= 10·098(15), b= 18·788(20), c= 36·712(36)Å, and Z= 8. The structure was solved by packing considerations and was refined to R 11·9% for the 1584 independent nonzero reflections. The asymmetric unit consists of two half-anions of [Fe6(CO)16C]2–(the remaining halves being generated by crystallographic mirror planes) and two [Me4N]+ cations. The [Fe6(CO)16C]2– anion has 13 terminal carbonyl ligands [two per iron atom, except for Fe(4) which bears three], and 3 ‘semi-bridging’ carbonyls. Nonbridged Fe–Fe bonds range from 2·646(10) to 2·743(10)Å, bridged Fe–Fe bonds from 2·553(10) to 2·632(10)Å. The encapsulated carbido-carbon atom is octahedrally co-ordinated to six iron atoms, with individual Fe–C distances from 1·805(38) to 1·968(38)Å.