Ternary Compounds in the Sn-Rich Section of the Ba–Ga–Sn System: Ba8Ga16–xSn30+x (1.1 ≤ x ≤ 2.8) Clathrates of Type-I and？Type-VIII, and BaGa2–xSn4+x (x ≈ 0.2) with a Clathrate-like Structure

Systematic syntheses in the Ba–Ga–Sn system confirmed the existence of a new ternary phase BaGa 1.79Sn 4.21(2) (EuGa 2Ge 4 structure type; orthorhombic space group Cmcm, Pearson symbol oS28) with lattice parameters a = 4.5383(6) ？, b = 12.2486(16) ？, c = 14.3747(19) ？. The structure is best viewed as an open-framework based on tetrahedrally coordinated Sn/Ga atoms with Ba atoms enclosed in the voids within it. The new phase co-precipitates with two other compounds with very similar compositions—Ba 8Ga 14.5Sn 31.5(4) (K 4Si 23 structure type; cubic space group , Pearson symbol cP54; a = 11.6800(12) ？), and Ba 8Ga 13.2Sn 32.8(3), (Eu 4Ga 8Ge 15 structure type; cubic space group , Pearson symbol cI54; a = 11.5843(7) ？). Detailed discussion on how syntheses affect the crystal chemistry, and the temperature dependence of the atomic displacement parameters, obtained from single-crystal structure refinements, are also reported in this article.