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

Shiny crystals of the isotypic title compounds are obtained in high yield from suitable proportions of AH2, metal A, and Sn or Pb in welded Ta containers slowly cooled from 1100 °C. These were characterized by single-crystal X-ray diffraction for Ca3SnH2 and Ca3PbH2 (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 Ca3Tt 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)3Tt-4(H-)2. Their structure may be derived from the hexagonal version of the cubic perovskitic Ca3SnO by distortions that split the octahedral site in the oxide into edge-sharing tetrahedral pairs.