Synthesis and Characterization of A₃Na₁₀Sn₂₃ (A = Cs, Rb, K) with a New Clathrate-Like Structure and of the Chiral Clathrate Rb₅Na₃Sn₂₅

Four new compounds Cs17.4(1)Na60.6(1)Sn138 (1), Rb19.1(1)Na58.9(1)Sn138 (2), K21.3(1)Na56.7(1)Sn138 (3), and Rb20Na12Sn100 (4) were synthesized by fusion of the corresponding elements. The structures were determined by single-crystal X-ray diffraction. Compounds 1−3 are isostructural and crystallize in a new structure type (rhombohedral, R3̄m, Z = 1, a = 12.4567(9) Å, c = 51.533(3) Å for 1; a = 12.465(1) Å, c = 51.085(3) Å for 2; a = 12.456(2) Å, c = 50.559(4) Å for 3). The structure contains layers of fused pentagonal dodecahedra of tin that alternate with layers of isolated tin tetrahedra. It is an intergrowth between the structure of clathrate-II (A24Sn136) with the same layers of pentagonal dodecahedra and the Zintl phase ASn with Sn44- tetrahedra. Compound 4 is a new chiral clathrate (cubic, P4132, Z = 1; a = 16.4127(7) Å) with stoichiometry that corresponds to an electronically balanced Zintl phase.