Substitution Effects in Zintl Phases: Synthesis and Crystal Structure of the Novel Phases Ae 3 Sn 4−x Bi 1+x (x ≤ 1; Ae = Sr, Ba) Containing Shubnikov‐Type Nets $^{2}_{\infty}\rm [Sn_{4-x}Bi_{x}]$

The compounds Ae 3 Sn 4−x Bi 1+x (Ae = Sr, Ba) with x < 1 have been synthesized by solid‐state reactions in welded Nb tubes at high temperature. Their structures were determined by single crystal X‐ray diffraction studies to be tetragonal; space group I 4 /mcm (No. 140); Z = 4, with a = 8.968(1) Å, c = 12.859(1) Å for Sr 3 Sn 3.36 Bi 1.64(3) ( 1 ) and a = 9.248(2), c = 13.323(3) Å for Ba 3 Sn 3.16 Bi 1.84(3) ( 2 ). The structure consists of two interpenetrating networks formed by a 3D Ae 6/2 Bi substructure (anti‐ReO 3 type) forming the host, and layers of interconnected four‐member units [Sn 4−x Bi x ] with “butterfly”‐like shape as the guest. According to the Zintl‐Klemm concept, the compounds are slightly electron deficient and will be charge balanced for x = 1. The electronic structures of Ae 3 Sn 4−x Bi 1+x calculated by the TB‐LMTO‐ASA method indicate that the compounds correspond to ideal semiconducting Zintl phases with a narrow band gap for x = 1 (zero‐gap semiconductor). The origin of the slight deviation from the optimal electron count for a valance compound is discussed.