Nine Hexagonal Ca5Pb3Z Phases in Stuffed Mn5Si3-Type Structures with Transition Metal Interstitial Atoms Z. Problems with Classical Valence States in Possible Zintl Phases

Ternary hexagonal Ae5Tt3Z phases have been obtained from high-temperature reactions (1000-1300 °C in Ta) only for Ae (alkaline-earth metal) = Ca, Tt (tetrel) = Pb, and Z = V, Cr, Mn, Fe, Co, Ni, Zn, Ru, or Cd. The hexagonal crystal structures (stuffed Mn5Si3-type, P63/mcm, Z = 2) were refined for Z = Mn and Fe (a = 9.3580(3), 9.3554(5) (angstrom), c = 7.009(1), 7.009(1) (angstrom), respectively). In contrast, Ca5Pb3Z for Z = Cu or Ag form only with a trigonal structure (Pc1, Z = 2, a = 9.4130(3) (angstrom), c = 7.052(1) (angstrom) for Cu) in which regular displacements of only the linear strings of Ca1 atoms occur.