AN ELECTRIDE WITH A LARGE 6-ELECTRON RING

ELECTRIDES are crystalline salts that contain complexed alkali metal c ations whose charge is balanced by trapped electrons(1). Theory(2,3) a nd experiment(4,5) indicate that the excess electron distribution is c oncentrated in cavities and channels formed by close-packing of the la rge complexed cations. Thus electrides might serve as models of a conf ined electron gas. Only three electrides have been structurally charac terized previously(6-8). Here we report the structure of a new electri de, [Cs+(15C5) (18C6).e(-)](6).(18C6), where 15C5 and 18C6 represent c rown ethers with five and six oxygen atoms respectively. The unit cell has threefold symmetry, with a central 18C6 molecule surrounded by si x Cs+ cations, each sandwiched between a 15C5 and 18C6 molecule. The s ix electrons released from-the Cs/crown ether interaction seem to be t rapped in six cavities which form a puckered ring, three above and thr ee below the plane of the central 18C6 molecule. The ground state is d iamagnetic. This ring-like distribution of electrons contrasts with th e chain-like connections between electron cavities observed in other e lectrides(6-8). Polycrystalline samples of this new electride have an electrical conductivity about a million times greater than those of th e electrides Cs+(15C5)(2).e(-) and Cs+(18C6)(2).e(-). The size, shape and connectivity of the electron-containing cavities and channels evid ently exert a critical influence on the properties of electrides.