Abstract: Although a number of salts with alkali-metal anions (alkalides) or trapped electrons (electrides) are known, previously all were thermally unstable to irreversible decomposition of the cation complexant (crown ether or cryptand). By using the fully methylated nitrogen analogue of 18-crown-6, hexamethyl hexacyclen (HMHCY), two crystalline sodides, K+(HMHCY) Na-(I) and Cs+(HMHCY) Na-(11), have been synthesized and their crystal ...