Synthesis, X-ray single-crystal structure determination, and magnetic properties of [Rb(benzo[18]crown-6)]⁺ salts containing well-ordered fulleride trianions C₆₀^3-

Crystals of the composition [Rb(benzo[18]crown-6)]₃[η ³-C₆₀](C₇H₈)-(C₃H ₇NO)_4.5 (1) and [Rb-(benzo[18]crown-6)]₃[C ₆₀](C₃H₇NO)_5.33-(C₄H ₈O)_1.66 (2) were synthesized by reduction of C ₆₀ with elemental rubidium in a mixture of dimethylformamide/ tetrahydrofuran in the presence of benzo[18]crown-6. X-ray single-crystal structure determinations reveal well-ordered C₆₀ trianions in both compounds. In contrast to previously reported structures of compounds containing C₆₀^3- ions the present structure refinements allow the description of the buckyballs with good resolution (R₁/ wR ₂ for I > 2σ(I) (all data) are 0.030/ 0.069 (0.051/0.071) and 0.042/0.101 (0.076/0.108) for 1 and 2, respectively). In 1 the C ₆₀^3- unit coordinates in an refashion to one Rb atom, whose coordination sphere is completed by one benzo[18]crown-6 and one dimethylformamide molecule. In 2 no coordination of the alkali metal atom to the C₆₀ trianion is observed. Magnetic measurements for 1 reveal a magnetic moment of 1.74 μ_B, as expected for an isolated S = 1/2 spin system. The high-quality data of the present studies allowed a comparison of structural details of C₆₀^3- ions with other C ₆₀^n- units (n = 0, 2, 3) and a discussion of the structural Jahn-Teller distortions.