Structure and Properties of Li+(Cryptand [2.1.1])e-, an Electride with a 1D "Spin-Ladder-like" Cavity-Channel Geometry

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• 作者：Rui H. Huang ; Michael J. Wagner ; Deborah J. Gilbert ; Kerry A. Reidy-Cedergren ; Donald L. Ward ; Margaret K. Faber ; and James L. Dye
• 刊名：Journal of the American Chemical Society
• 出版年：1997
• 出版时间：April 23, 1997
• 年：1997
• 卷：119
• 期：16
• 页码：3765 - 3772
• 全文大小：375K
• 年卷期：v.119,no.16(April 23, 1997)
• ISSN：1520-5126

文摘

The title electride crystallizes in the orthorhombic space groupPbcn with a = 10.060(4) Å, b= 23.134(8) Å, c = 8.380(4) Å, and z = 4.A second powdered phase of unknown structure, but with ratherdifferent properties,forms when rapidly precipitated "seed" powder is used. Thecrystalline phase contains electron-trapping cavities,each of approximate diameter 4.3 Å, connected in zigzag fashion alongthe c axis by rather open channels of minimumdiameter 2.4 Å (center-to-center distance 7.9 Å). Each cavity isalso connected to next-neighbor cavities, 8.2 Åaway along c, by channels of diameter 1.5 Å.Inter-chain channels are <1.0 Å in diameter so that thecavity-channel structure is well-described as "ladder-like". Replacingthe trapped electron by Na^- in thecorrespondingsodide, Li⁺ (cryptand [2.1.1])Na^-,results in an orthorhombic structure (space groupPna2₁). Although the anionicsites in the sodide are only slightly bigger than those in theelectride, the channel structure is markedly different,forming a 3-dimensional network. The magnetic susceptibilities ofboth phases of the electride above 14 K arewell-fit by the linear chain Heisenberg antiferromagnetic model withvalues of J/k_B of -54 (crystals)and -17.8 K(powder). Both types show marked deviations below 14 K towardgreater spin-pairing. This behavior was verifiedby EPR measurements of intensity vs temperature. Theelectride was characterized further by two probe pressedpellet conductivity, variable temperature ⁷Li MAS-NMR,and DSC.