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 Rb20Na12-Sn-100 (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, R (3) over barm, Z = 1, a = 12.4567(9) Angstrom, c = 51.533(3) Angstrom for 1; a = 12.465(1) Angstrom, c = 51.085(3) Angstrom for 2; a 12.456(2) Angstrom, c = 50.559(4) Angstrom 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 (A(24)Sn(136)) With the same layers of pentagonal dodecahedra and the Zintl phase ASn with Sn-4(4-) tetrahedra, Compound 4 is a new chiral clathrate (cubic, P4(1)32, Z = 1; a 16.4127(7) Angstrom) with stoichiometry that corresponds to an electronically balanced Zintl phase.