Structure and Bonding of Li1.42(5)Pd2Sn5.58(5): A Lithium Intercalated Palladium Stannide

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• 作者：Puravankara Sreeraj ; Rolf-Dieter Hoffmann ; Zhiyun Wu ; Rainer Pö ; ttgen ; and Ulrich Hä ; ussermann
• 刊名：Chemistry of Materials
• 出版年：2005
• 出版时间：February 22, 2005
• 年：2005
• 卷：17
• 期：4
• 页码：911 - 915
• 全文大小：189K
• 年卷期：v.17,no.4(February 22, 2005)
• ISSN：1520-5002

文摘

The ternary stannide Li_1.42(5)Pd₂Sn_5.58(5) was synthesized from the elements by induction melting in asealed tantalum tube in a water-cooled quartz sample chamber. Li_1.42(5)Pd₂Sn_5.58(5) was characterized byX-ray powder and single-crystal diffraction: P4/mbm, a = 662.61(7) pm, c = 843.39(10) pm, V =0.3703 nm³, Z = 4, wR2 = 0.0388, 477 F² values, and 17 variable parameters. It crystallizes with a newstructure type that is closely related to the slightly orthorhombically distorted binary stannide PdSn₃.The palladium atoms in Li_1.42(5)Pd₂Sn_5.58(5) have a square antiprismatic tin coordination. The squareantiprisms are condensed via common edges and faces forming [Pd₂Sn₆] double layers in a simple stackingsequence which leaves square prismatic voids for the lithium atoms. Syntheses with different startingcompositions always resulted in the same refined composition Li_1+xPd₂Sn_6-x (x = 0.40-0.46) for thesingle crystals investigated. The tin sites within the double layers reveal an appreciable amount of Sn/Limixing for six crystals investigated, in agreement with EDX data. First principles electronic structurecalculations were employed to analyze the bonding situation and the nature of the Sn/Li mixed occupancyin Li_1+xPd₂Sn_6-x. It was found that by reducing the electron count of LiPd₂Sn₆, which can be achievedby a partial replacement of Sn by Li, the Fermi level is shifted to a dip in the density of states. This isa favorable situation and the corresponding electron count leads to a composition Li_1.45Pd₂Sn_5.65, whichis very close to the experimentally found value. The location of this dip coincides with a turnover ofPd-Sn and Sn-Sn interactions from being bonding/nonbonding to being antibonding.