Structure and properties of a new electride, Rb+(cryptand[2.2.2])e(-)

This is the sixth electride whose crystal structure has been determined and the fourth to show polymorphism. Crystals of the title electride prepared from mixed solvents have a structure similar to that of Li+(cryptand[2.1.1] )e(-). Electrons occupy cavities that are connected by "ladder-like" channe ls. The static and spin magnetic susceptibilities of polycrystalline sample s that contain this polymorph (called phase alpha) show Heisenberg 1D antif erromagnetic behavior with -J/k(B) = 30 K. Similar to other electrides with "localized" electrons, this electride is a poor conductor (sigma < 10(-4) ohm(-1)cm(-1)). Thin films prepared by high vacuum co-deposition of Rb meta l and cryptand[2.2.2] have optical spectra and near-metallic electrical con ductivity nearly identical with these of K+(cryptand[2.2.2])e(-). These pro perties would not be expected if the film structure were the same as that o btained for crystals. Rather, they suggest that the films consist of microc rystals whose structure is similar to that of K+(cryptand[2.2.2])e(-). Poly crystalline samples prepared by slow evaporation of methylamine from stoich iometric solutions at -78 degrees C (called phase beta) have properties sim ilar to those of K+(cryptand[2.2.2])e(-). The conductivity of samples that contain phase beta is more than an order of magnitude larger than those wit h phase a. Magnetic and spin susceptibilities show that phase beta samples have much larger electron-electron interactions. As with K+(cryptand[2.2.2] )e(-), the maenetic susceptibility of phase beta is compatible with alterna ting linear chain Heisenberg antiferromagnetism, with -J/k(B) approximate t o 300 K and -J'/k(B) approximate to 240 K. Thin vapor co-deposited films sh ow abrupt changes in the conductivity and optical spectrum at -12 degrees C that suggest a transition that may be conversion of phase beta to phase al pha.