Formation of Ion Pairs in Rubidium-Tetrahydrofuran Crown Ether Solutions

Article abstract of DOI:10.1021/j100445a009

The effect of dicyclohexyl-18-crown-6 (CR) on the transient species formed in irradiated solutions (pulse radiolysis) of THF saturated with rubidium metal was investigated.Analysis of the kinetics and spectra of the transients reveals that, in addition to the metal anion Rb^-, the solvated monomer Rb^., and the solvated electron e_s^-, a new species attributed to an ion pair of the type (RbCR⁺,e) is formed in solutions containing CR.This species is characterized by its absorption spectrum and its formation by a second-order process, Rb^. + CR <*> (RbCR⁺,e).The absorption spectrum of Rb^. is peaked around 1250 nm and that of (RbCR⁺,e) around 1800 nm, with molar extinction coefficients being 2.4E4 M^-1 cm^-1 and 2.8E4 M^-1, respectively.It is concluded that the addition of CR to THF is equivalent to the increase in the donor number of the solvent in which the alkali metal is dissolved.