Synthesis, crystal structure and chemical bonding of a new La–In–Ge ternary phase: La 11In 6Ge 4

Abstract

The new tetragonal phase La 11In 6Ge 4 is obtained from high temperature reactions of the pure elements in welded Ta tubes. Its crystal structure was established by single-crystal X-ray diffraction in the tetragonal space group I4/mmm (No. 139), with cell parameters of a=12.073(2), and c=16.829(3) Å. The structure of La 11In 6Ge 4 may be derived from the Ho 11Ge 10 structure type by replacing Ge atoms of the Ge 4 squares and Ge 2 dimers in Ho 11Ge 10 with indium. However, the nominal squares and dimers in Ho 11Ge 10 are no longer isolated fragments in La 11In 6Ge 4, but are linked via In–In bonds (3.222(3) Å), resulting in a three-dimensional In anionic network. The chemical bonding of the new ternary phase can be formulated according to the Zintl concept as La 11) 33+ Ge 4 isolated) 16− In 6 network) 17−. Extended-Hückel band structure calculations on the [In 6] 17− network indicate that the compound may be considered a ‘metallic’ Zintl phase with the valence bands having an electronic count associated with an electron-precise [In 6] 14− network of In 4 squares and In 2 units. The remaining electrons occupy conduction bands that represent anti-bonding interactions within the In 2 fragments, and between the In squares and dimers.