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

Chemistry. 2009;15(13):3261-7. doi: 10.1002/chem.200801923.


Finally, a structure with well-resolved C(60) (3-) ions and S=1/2 spin system: The two novel title compounds have clearly S=1/2 and not S=3/2 electronic states, as expected for the occupation of the triply degenerate LUMO of C(60.) These structures with well-ordered fullerene trianions show that the expected Jahn-Teller distortion is not observable in X-ray diffraction experiments.Crystals of the composition [Rb(benzo[18]crown-6)](3)[eta(3)-C(60)](C(7)H(8))(C(3)H(7)NO)(4.5) (1) and [Rb(benzo[18]crown-6)](3)[C(60)](C(3)H(7)NO)(5.33)(C(4)H(8)O)(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>2sigma(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.