Negatively Charged Iron-Bridged Fullerene Dimer {Fe(CO)2-μ2-η2,η2-C60}22

The interaction of {Cryptand(K⁺)}(C₆₀^•-) with Fe₃(CO)₁₂ produced {Cryptand(K⁺)}₂{Fe(CO)₂-μ₂-η²,η²-C₆₀}₂^2-·2.5C₆H₄Cl₂ (1) as the first negatively charged iron-bridged fullerene C₆₀ dimer. The bridged iron atoms are coordinated to two 6-6 bonds of one C₆₀ hexagon with short and long C(C₆₀)-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 Fe₂(CO)₄ units, which causes a 50 cm^-1 shift of the C≡O vibration bands to smaller wavenumbers, and the C₆₀ 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 C₆₀ ligand.

Electrochemically Induced Dimerization of p9mp-C70(CF3)12 Trifluoromethylated Fullerene

We report a comprehensive study of a novel isomer of C₇₀(CF₃)₁₂, p⁹mp-C₇₀(CF₃)₁₂, whose electrochemical behavior differs from most of the other trifluoromethylated fullerenes. The addition pattern of p⁹mp-C₇₀(CF₃)₁₂ is established by means of ¹⁹F-¹⁹F COSY NMR spectroscopy and DFT calculations. Like p⁷mp-C₇₀(CF₃)₁₀, the new isomer p⁹mp-C₇₀(CF₃)₁₂ undergoes dimerization to the [C₇₀(CF₃)₁₂]₂^2- upon single-electron reduction. The electrochemical observations are supported by the DFT calculations of dimerization energy and the temperature dependence of the CW X-band EPR spectroscopy data. Experimentally determined dimerization energies of p⁹mp-C₇₀(CF₃)₁₂^-• and p⁷mp-C₇₀(CF₃)₁₀^-• in solution are ca -8 and -26 kJ mol^-1, respectively, in good correspondence with DFT data.

Molecular Structure and Magnetic and Optical Properties of Endometallonitridofullerene Sc3 N@Ih -C80 in Neutral, Radical Anion, and Dimeric Anionic Forms

A series of compounds with Sc₃ N@I_h -C₈₀ in the neutral, monomeric, and dimeric anion states have been prepared in the crystalline form and their molecular structures and optical and magnetic properties have been studied. The neutral Sc₃ N@I_h -C₈₀ ⋅3 C₆ H₄ Cl₂ (1) and (Sc₃ N@I_h -C₈₀ )₃ (TPC)₂ ⋅5 C₆ H₄ Cl₂ (2, TPC=triptycene) compounds both crystallized in a high-symmetry trigonal structure. The reduction of Sc₃ N@I_h -C₈₀ to the radical anion resulted in dimerization to form diamagnetic singly bonded (Sc₃ N@I_h -C₈₀ ^- )₂ dimers. In contrast to {[2.2.2]cryptand(Na⁺ )}₂ (Sc₃ N@I_h -C₈₀ ^- )₂ ⋅2.5 C₆ H₄ Cl₂ (3) with strongly disordered components, we synthesized new dimeric phases {[2.2.2]cryptand- (K⁺ )}₂ (Sc₃ N@I_h -C₈₀ ^- )₂ ⋅2 C₆ H₄ Cl₂ (4) and {[2.2.2]cryptand- (Cs⁺ )}₂ (Sc₃ N@I_h -C₈₀ ^- )₂ ⋅2 C₆ H₄ Cl₂ (5) in which only one major dimer orientation was found. The thermal stability of the (Sc₃ N@I_h -C₈₀ ^- )₂ dimers was studied by EPR analysis of 3 to show their dissociation in the 400-460 K range producing monomeric Sc₃ N@I_h -C₈₀ ^.- radical anions. This species shows an EPR signal with a hyperfine splitting of 5.8 mT. The energy of the intercage C-C bond was estimated to be 234±7 kJ mol^-1 , the highest value among negatively charged fullerene dimers. The EPR spectra of crystalline (Bu₃ MeP⁺ )₃ (Sc₃ N@I_h -C₈₀ ^.- )₃ ⋅C₆ H₄ Cl₂ (6) are presented for the first time. The salt shows an asymmetric EPR signal, which could be fitted by three lines. Two lines were attributed to Sc₃ N@I_h -C₈₀ ^.- . Hyperfine splitting is manifested above 180 K due to the hyperfine interaction of the electron spin with the three scandium atoms (a total of 22 lines with an average splitting of 5.32 mT are observed at 220 K). Furthermore, each of the 22 lines is additionally split into six lines with an average separation of 0.82 mT. The large splitting indicates intrinsic charge and spin density transfer from the fullerene cage to the Sc₃ N cluster. Both the monomeric and dimeric Sc₃ N@I_h -C₈₀ ^- anions show an intrinsic shift of the IR bands attributed to the Sc₃ N cluster and new bands corresponding to these species appear in the NIR range of their UV/Vis/NIR spectra, which allows these anions to be distinguished from neutral species.

Optical and magnetic properties of trans-indigo˙− radical anions. Magnetic coupling between trans-indigo˙− (S = 1/2) mediated by intermolecular hydrogen N–H⋯OC bonds

Reduction of trans-indigo yields salt {cryptand[2.2.2](K⁺)}₆{trans-indigo}₇·5.5C₆H₄Cl₂ (1). The trans-indigo˙⁻ radical anions are bonded by intermolecular hydrogen N–H⋯OC bonds of 2.11–2.17 Å.