New Chemical Method for Selective Generation of C70n- (n = 1, 2, 3) Anions and Formation and Properties of an Aqueous Colloidal Solution of C70.

Facile methods for selective generation of C70n– (n = 1, 2, 3) and preparation and properties of an aqueous colloidal solution of C70 are reported. C70 was reduced by Al–Ni alloy (or Zn, Sn) to obtain C70–, C702–, C703– in aqueous caustic–THF or mixtures of DMSO and THF with varying compositions, without the need for stoichiometric control of the reducing agents. The reduction products were confirmed by ESI–MS, VIS–NIR and EPR spectra. C70n– (n = 1, 2, 3) are stable to water under our experimental conditions, but very sensitive to oxygen. The oxidation reaction of C70– with oxygen follows C70–→C70, but oxidation of C703– follows C703–→C702–→C70(OH)x, which was monitored by NIR absorption spectra and species characterized by FT–IR and 1H NMR. The C70 sol is formed while C70– is oxidized in aqueous solution. The sol is composed of C70 which was confirmed by UV, FTIR and APCI–MS. The aqueous colloidal solution of C70 possesses excellent optical limiting properties and biological activity, illustrated by strong cytotoxicity to U937 cells upon visible light irradiation.