Intermetallic Hydrides as Zintl Phases:  A₃TtH₂ Compounds (A = Ca, Yb; Tt = Sn, Pb) and Their Structural Relationship to the Corresponding Oxides

Abstract

Shiny crystals of the isotypic title compounds are obtained in high yield from suitable proportions of AH(2), metal A, and Sn or Pb in welded Ta containers slowly cooled from 1100 degrees C. These were characterized by single-crystal X-ray diffraction for Ca(3)SnH(2) and Ca(3)PbH(2) (orthorhombic, Cmcm (No. 63), Z = 4, a = 8.866(1), 8.937(1) Å, b = 11.371(2), 11.470(2) Å, c = 5.220(1), 5.2551(7) Å, respectively). The structure contains distorted hcp layers of Ca(3)Tt between which hydrogen occupies all tetrahedral voids formed by Ca atoms. These tetrahedra share three edges to form double chains along the c axis that are separated by Tt atoms. Both calcium compounds are diamagnetic semiconductors, and the family can all be formulated in terms of oxidation states as Zintl phases (A(+2))(3)Tt(-4)(H(-))(2). Their structure may be derived from the hexagonal version of the cubic perovskitic Ca(3)SnO by distortions that split the octahedral site in the oxide into edge-sharing tetrahedral pairs.