A Silicon Strand of More than 7 A in Diameter in Ba_2Eu_3Si_7

摘要

The binary compounds formed by silicon with alkaline-earth and rare-earth metals differ substantially in their crystal structures, as well as in their stoichiometries and physical properties. Barium forms the five stable silicides BaSi_2, Ba_3Si_4, BaSi, Ba_5Si_3 ,and Ba_2Si, whereas only two europium compounds, EuSi_2 and EuSi, are yet known. Except for BaSi and EuSi, both of which crystallize in the CrB structural type with planar, one-dimensional zigzag chains _(infinity)~1[Si~(2-)], there are noother direct structural relationships between Eu and Ba silicides BaSi_2 contains isolated Si_4~(4-) tetrahedta, whereas a three-dimensional Si skeleton of three-bonded (3b), trigonal-planar Si atoms is present in EuSi_2. A Si_4~(6-) butterfly anion occurs in Ba_3Si_4, which according to the Zintl-Klemm concept is a reduced form of the tetrahedron.