Jn. Kim et al., RB-87, RB-85, AND K-39 NMR-STUDIES OF ALKALIDES, ELECTRIDES, AND RELATED-COMPOUNDS, Journal of physical chemistry, 100(8), 1996, pp. 2885-2891
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.