Structural and electronic characterization of Eu2LiSi 3, Eu2LiGe3 and EuxSr 2-xLiGe3 mixed crystals

Abstract

The new rare earth metal Zintl phases Eu2LiSi3, Eu2LiGe3 and the solid solution EuxSr 4-xLi2Ge6 have been synthezised by solid state inert gas techniques and their crystal structures been determined from single crystals. Eu2LiSi3 crystallizes in an own structure type which has close relations to the ThSi2 type with lithium being situated on silicon vacancies. This generates a new kind of planar Zintl anion which has an all trans linear chain backbone and terminal Si side groups at half of the silicon atoms of the chain. Eu2LiGe3 forms the α-Ca2LiSi3 structure with an unbranched planar polymeric Zintl anion which has a cis-trans conformation of the kind (tttctc)n. Both of the polyanions [Si3]5- and [Ge3]5-, respectively are unsaturated with an underoccupied π* system leaving one residual π bond per three Tt atoms (Tt = Si, Ge). Features of the crystal and of the electronic structures are being analysed based on geometrical and on band structure considerations. DOS, partial DOS, Mulliken overlap populations and calculations of the electron localization function (ELF) based on Extended Hückel and on LMTO calculations confirm the bonding structure and reveal preferred localizations of the π bonds. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.