Negatively Charged Iron-Bridged Fullerene Dimer {Fe(CO)-μ-η,η-C}.

The interaction of {Cryptand(K)}(C) with Fe(CO) produced {Cryptand(K)}{Fe(CO)--,-C}·2.5CHCl () as the first negatively charged iron-bridged fullerene C dimer. The bridged iron atoms are coordinated to two 6-6 bonds of one C hexagon with short and long C(C)-Fe bonds with average lengths of 2.042(3) and 2.088(3) Å. Fullerenes are close to each other in the dimer with a center-to-center interfullerene distance of 10.02 Å. Optical spectra support the localization of negative electron density on the Fe(CO) units, which causes a 50 cm shift of the C≡O vibration bands to smaller wavenumbers, and the C cages. Dimers are diamagnetic and electron paramagnetic resonance silent and have a singlet ground state resulting from the formation of an Fe-Fe bond in the dimer with a length of 2.978(4) Å. According to density functional theory calculations, the excited triplet state is higher than the ground state by 6.5 kcal/mol. Compound shows a broad near-infrared band with a maximum at 970 nm, which is attributable to the charge transfer from the orbitals localized mainly on iron atoms to the C ligand.