The chemical dynamics of Na-in liquid 12-crown-4 solutions deduced from23Na nuclear spin relaxation rates

Abstract

Solutions containing the sodium anion (Na-) were prepared by dissolving either NaK, NaRb or NaCs alloys in liquid 12-crown-4, 12C4. The 23Na nuclear spin-lattice (T 1n ) and spin-spin (T 2n ) relaxation times of the N.M.R. signal originating from Na- have been measured as a function of temperature, concentration and counter-cation K+, Rb+ or Cs+. The details of the inequality between T 1n and T 2n shown that the lifetime of Na- is limited by a two-step process. In the first step a strong complex of an alkali cation and 12C4 molecules dissociates to yield an uncomplexed cation to which one 3s electron from Na- is transferred in the second step. The 23Na nuclear spin relaxation data are combined with the results of previous EPR and pulse radiolysis experiments to deduce both the reactions generating Na- as well as further equilibria involving both complexed and uncomplexed cations, solvated electrons and a variety of paramagnetic species containing an electron and a cation.