Über die Kristallstrukturen der Tellurate Pb3Fe2Te2O12 und Pb2CoTeO6 / On the Crystal Structures of the Tellurates Pb3Fe2Te2O12 and Pb2CoTeO6

Pb 3 Fe 2 Te 2 O 12 (I) and Pb 2 CoTeO 6 (II) have been prepared by crystallization from melts. Single crystal X-ray investigations led to monoclinic (I) and tetragonal (II) symmetry, space groups C 4 s -Cc and D 17 4h -14/mmm. Lattice constants I: a = 9.866(3), b = 15.332(4), c = 7.172(2) Å, β = 111.34(3)°, Z = 4. II: a = 5.661(5), c = 8.004(7) Å, Z = 2. (I) represents a new crystal structure, characterized by a network of octahedra occupied by Fe 3+ and Te 6+ in a disordered manner. The centres of negative charge of the lone pairs of Pb 2+ in I are estimated by Coulomb term calculations. II belongs to the elpasolithe type