Synthesis and Structure of Ba₂Sn₃Sb₆, a Zintl Phase Containing Channels and Chains

The new Zintl phase dibarium tritin hexaantimonide, Ba2Sn3Sb6 has been synthesized, and its structure has been determined by single-crystal X-ray diffraction methods. It crystallizes in the orthorhombic space group -Pnma with a = 13.351(1) Å, b = 4.4100(5) Å, c = 24.449(3) Å, and Z = 4 (T = −50 °C). The structure of Ba2Sn3Sb6 comprises large channels [010] defined by 30-membered rings constructed from an anionic framework. This framework is built up from Sn-centered trigonal pyramids and tetrahedra, as well as zigzag chains of Sb atoms. Within the channels reside the Ba2+ cations and additional isolated zigzag Sb−Sb chains. The simultaneous presence of Sn trigonal pyramids and tetrahedra implies that Ba2Sn3Sb6 is a mixed-valence compound whose oxidation state notation can be best represented as (Ba2+)2[(SnII)2(SnIV)(Sb-III)3(Sb-I)]2-[(Sb-I)2]2-.