Coordination chemistry of polynitriles. Part 9. Decacyanoferrocene revisited: crystal and molecular structure of cis-[{C5(CN)5}2(MeCN)4Fe].

The reaction of Ag[C5(CN)5] with anhydrous FeCl2 in acetonitrile leads to colourless crystals of tetrakis(acetonitrile-κN)bis(pentacyanocyclopentadienido-κN)iron(II) acetonitrile 1.8-solvate, [Fe(C10N5)2(CH3CN)4]·1.8CH3CN or cis-[{C5(CN)5}2(MeCN)4Fe]·1.8MeCN. The compound crystallizes in the triclinic space group P-1 as monomers, which exhibit weak C-H...N and π-π interactions. The crystals contain ca 20% solvent-accessible voids, which are nearly completely filled by two MeCN molecules.