MULTINUCLEAR ENDOR STUDY OF TRAPPED ELECTRONS IN THE POLYCRYSTALLINE SODIDE CS+(HMHCY).NA-

Synthesis of the sodide Cs+(HMHCY).Na-, in which HMHCY is the cation complexant hexamethylhexacyclen [Kuchenmeister, M. E.; Dye, J. L. J. Am. Chem. Soc. 1989, 111, 935], always leads to the inclusion of trapped electrons. The nature of the trapping site has been explored by EPR and multinuclear ENDOR techniques. Pronounced axial hyperfine coupling to a single cesium nucleus is in accord with an F-center model in which Na- vacancies are occupied by trapped electrons. Dipolar and contact coupling to -CH3 protons as measured by H-1 ENDOR studies of the protio- and deuteriomethyl compounds is also in accord with this model. ENDOR signals from Na-23 and Cs-133 reflect the NMR powder patterns of these nuclei and correspond to small Fermi contact densities (0.079 and 0.014 or 0.091 and 0.018% atomic character, respectively, depending on the choice of sign for the hyperfine coupling constant) resulting from the ''tails'' of the trapped electron distribution. It is suggested that electron trapping in alkalides is similar to that which occurs at all anionic sites in electrides.