Alkaline-Earth-Metal Antimonides and Bismuthides with the A(5)Pn(3) Stoichiometry. Interstitial and Other Zintl Phases Formed on Their Reactions with Halogen or Sulfur

The phase ABPn(3) (A = Ca, Sr, or Ba; Pn = Sb or Bi) have been synthesized in high yield in welded Ta containers and confirmed to have either the Mn6Si3 (M) or the beta-Yb6Sb3 (Y) structure types, or both. Lattice constants from Guinier powder diffraction suggest most previous reports on these phases probably pertained to binary compounds. These phases in the presence of chlorine or, where attempted, bromine form Zintl phases A(5)Pn(3)X (X = Cl, Br) in the same M structure but with halogen in all octahedral cavities of the confacial A(6/2)Pn(6/2) chains. Two chlorides were studied by single-crystal means (space group P6(3)/mcm; Ca5Sb3Cl: a = 9.0805 (3) angstrom, c = 7.0898 (6) angstrom, R/R-w = 3.8/5.9%; Ba5Sb3Cl: a = 10.062 (4) angstrom, c = 7.770 (6) angstrom, 5.1/8.9%). X-ray study of single-crystal SrBSb3 in the same structure type confirmed the stoichiometry and the absence of atoms in the interstitial cavity (a = 9.5037 (5) angstrom, c = 7.4095 (8) angstrom 3.2/2.9%). The M-type analogues Ce6Sb3Cl, Ce5Bi3Cl, and Ce6Bi3Br also form readily. Fluorine reacts with Ca6Sb3 and CaBBi3 but not BaBSb3 to form Y-type structure analogues with fluoride in a suitable tetrahedral cavity (space group Pnma; CaBSb3F: a = 12.442 (2) A, b = 9.653 (2) A, c = 8.381 (2) angstrom, R/R-w = 2.5/3.3; Ca5Bi3F: a = 12.602 (2) angstrom,b = 9.771 (2) angstrom, c = 8.501 (2) A, 6.0/5.8%). Reactions of CaBSb3 with the appropriate proportions of C, O, or S yield CaC2, the known Ca4Sb20, or the new valence compound Ba4Sb24S0.4 in a defect, anti-Th3P4 type structure (o = 9.6508 (3) angstrom). Iodine with Ba6Sb3 analogously yields a 2:1 proportion of Ba4Sb2SI0.5 (anti-Th3P4, (I) over bar(4) over bar 3d, a = 10.475 (7) angstrom, R/R-w = 8.8/10.0%) and Ba2SbI (disordered NaCl, a = 7.0970 (6) A).