Synthesis, X-ray Single-Crystal Structure Determination, and Magnetic Properties of [Rb(benzo[18]crown-6)]+ Salts Containing Well-Ordered Fulleride Trianions C603-

Crystals of the composition [Rb(benzo[18]crown-6)](3)[eta(3)-C-60](C7H8)-(C3H7NO)(4.5) (1) and [Rb(benzo[18]crown-6)](3)[C-60](C3H7NO)(5.33)-(C4H8O)(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 C-60 trianions in both compounds. In contrast to previously reported structures of compounds containing C-60(3-) ions the present structure refinements allow the description of the buckyballs with good resolution (R-1/wR(2) for I > 2 sigma(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 eta(3)-fashion 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 C-60 trianion is observed. Magnetic measurements for 1 reveal a magnetic moment of 1.74 mu(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 C-60(3-) ions with other C-60(n-) units (n=0, 2, 3) and a discussion of the structural Jahn-Teller distortions.