Three Salts Containing the Fullerene Tetra-Anion C604- - Synthesis, X-Ray Single-Crystal Structure Determination and EPR Investigation

A synthesis for four-fold negatively charged fullerides in solution is presented. Three salts containing discrete C-60(4-) anions were synthesized by the reduction of C-60 in solution using rubidium-mercury amalgams and rubidium suboxide both in the presence of elemental mercury. The three new salts, [Rb6DMF14(C6H13N2O2)(2)]center dot C-60 (1), [Rb(diaza-18-crown-6)](4)center dot C-60 center dot(en)(4.1) (2), and [Rb(benzo-18-crown-6)](4)center dot C-60 (3), were characterized by single-crystal X-ray diffraction. The results clearly indicate a charge of 4 for the fulleride anions. In 1 the fulleride units are ordered, and their distortion from I-h symmetry shows similarities to binary alkali metal fullerides that contain C-60(4-) anions. In the crystal structures of 2 and 3 the C-60(4-) anions show a rotational disorder. In all structures the 6:6 bond lengths within the fulleride are strongly enlarged compared to the ones in neutralC(60). EPR measurements reveal a singlet state for the C-60(4-) anion.