RB-87, RB-85, AND K-39 NMR-STUDIES OF ALKALIDES, ELECTRIDES, AND RELATED-COMPOUNDS

Alkali metal anions generally have narrow NMR lines that are only slig htly shifted from those calculated for the gaseous anion. When, howeve r, the anions form contact dimers, as in K+(cryptand[2.2.2]K- and Rb+( cryptand[2.2.2]Rb-, or chains, as in Rb+(18-crown-6Rb-, the NMR peak o f the alkali metal anion is significantly broadened and shifted parama gnetically. In order to obtain reliable quadrupole coupling constants, asymmetry parameters, and chemical shifts from polycrystalline sample s of alkalides and electrides, spin-echo Rb-87, Rb-85, and K-39 static NMR spectra were obtained for 9 alkalides, 3 electrides, and 11 model compounds. A puzzling distortion of the powder line shapes of two alk alides, an electride, and a model salt was traced to orientation-depen dent transverse relaxation times (T-2) by studies of the single-crysta l Rb-87 NMR spectra of Rb+(cryptand[2.2.2]Cl-. To analyze the NMR powd er patterns, a general computer program was developed and coupled to a nonlinear least-squares fitting program.