An electride with a large six-electron ring

Abstract

ELECTRIDES are crystalline salts that contain complexed alkali metal cations whose charge is balanced by trapped electrons1. Theory2,3 and experiment4,5 indicate that the excess electron distribution is concentrated in cavities and channels formed by close-packing of the large complexed cations. Thus electrides might serve as models of a confined electron gas. Only three electrides have been structurally characterized previously6–8. Here we report the structure of a new electride, [Cs + (15C5) (18C6).e-]6.(18C6), where 15C5 and 18C6 represent crown ethers with five and six oxygen atoms respectively. The unit cell has threefold symmetry, with a central 18C6 molecule surrounded by six Cs+ cations, each sandwiched between a 15C5 and 18C6 molecule. The six electrons released from the Cs/crown ether interaction seem to be trapped in six cavities which form a puckered ring, three above and three below the plane of the central 18C6 molecule. The ground state is diamagnetic. This ring-like distribution of electrons contrasts with the chain-like connections between electron cavities observed in other electrides6–8. Polycrystalline samples of this new electride have an electrical conductivity about a million times greater than those of the electrides Cs+ (15C5)2.e- and Cs+ (18C6)2.e-. The size, shape and connectivity of the electron-containing cavities and channels evidently exert a critical influence on the properties of electrides.