New chemical method for selective generation of C70n– (n = 1, 2, 3) anions and formation and properties of an aqueous colloidal solution of C70

Abstract

Facile methods for selective generation of C₇₀^n– (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^–, C₇₀^2–, C₇₀^3– 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. C₇₀^n– (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 C₇₀^3– follows C₇₀^3–→C₇₀^2–→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.