[CS+(15-CROWN-5)(18-CROWN-6)E(-)](6)CENTER-DOT(18-CROWN-6) - PROPERTIES OF THE FIRST MIXED CROWN ETHER ELECTRIDE

摘要

The sizes and structures of cavities and channels in the first crystalline mixed crown electride, [Cs+(18-crown-6)(15-crown-5)e(-)](6) .(18C6), are reported and related to its properties. The structure consists of cesium cations complexed by one each of the 18-crown-6 and 15-crown-5 complexants, which pack to leave a remarkable ring of six cavities that are presumed to be the trapping sites of the excess electrons. The sizes and shapes of the cavities and connecting channels are described in detail with the aid of a newly developed computer program. The magnetic susceptibility (corrected for the low-temperature ''tail'' due to defect electrons) is shown to be consistent with that expected for an antiferromagnetically coupled 6-electron ring and yields an estimate of the coupling strength, J/k, of similar to -410 K. Cs-133 MAS NMR and the temperature dependence of the magnetic susceptibility show that the electron density at the cation nucleus is an order of magnitude smaller than that of either Csf(18-crown-6)(2)e(-) or Cs+(15-crown-5)(2)e(-). The compound is moderately conductive with a lower limit of conductivity at 213 K estimated to be 2 x 10(-3) Omega(-1) cm(-1). The dominant conduction mechanism is probably variable range hopping of defect electrons. (C) 1995 Academic Press, Inc. [References: 37]