Negatively Charged Iron-Bridged Fullerene Dimer {Fe(CO) 2 -μ 2 -η 2 ,η 2 -C 60 } 2 2 .

The interaction of {Cryptand(K + )}(C 60 •- ) with Fe 3 (CO) 12 produced {Cryptand(K + )} 2 {Fe(CO) 2 - μ 2 - η 2 , η 2 -C 60 } 2 2- ·2.5C 6 H 4 Cl 2 ( 1 ) as the first negatively charged iron-bridged fullerene C 60 dimer. The bridged iron atoms are coordinated to two 6-6 bonds of one C 60 hexagon with short and long C(C 60 )-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 2 (CO) 4 units, which causes a 50 cm -1 shift of the C≡O vibration bands to smaller wavenumbers, and the C 60 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 1 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 60 ligand.