Synthesis and Crystal Structure Analysis of C₆₀ Fulleride Dianions in Solvates of [A([2.2.2]crypt)]₂ [C₆₀] (A = K, Rb, Cs)

Reduction of C₆₀ with the alkali metals A = K, Rb and Cs in tetrahydrofüran as a solvent and addition of [2.2.2]crypt [1], dimethylformamide and cyclohexane lead to the formation of crystalline samples of [A([2.2.2]crypt)]2[C₆₀](C₆H₁₂)₂(C₃H₇NO)₂(C₄H₈O)₂ (A = K, Rb, Cs) 1a, 1b and 1c as major fractions. As a by-product of compound 1a, a second minor fraction containing [K([2.2.2]crypt)]2[C₆₀](C₃H₇NO)4 2 was obtained. The structures of the four compounds have been determined by single-crystal X-ray analyses. The [C₆₀]²~ dianions are predominantly ordered. As the main structural motif the structures of compounds 1a, 1b and 1c contain pseudo-hexagonal layers of [C₆₀]^2- dianions. Compound 1c contains a rare example of a Cs⁺ sequestering [2.2.2]crypt molecule. The packing of the ionic units in compound 2 also shows layers of distorted hexagons formed by [C₆₀]^2- dianions which arranged in pairs with short contacts of io.3 Å between their centers of gravity.