Phase Formation Studies of Lead(II) Copper(II) Oxotellurates: The Crystal Structures of Dimorphic PbCuTeO₅, PbCuTe₂O₆, and [Pb₂Cu₂(Te₄O₁₁)](NO₃)₂

Abstract

Two modifications of the oxotellurate(VI) PbCuTeO5 were isolated as single crystals from product mixtures obtained from solid state reactions, whereas single crystals of the oxotellurates(IV) PbCuTe2O6 and [Pb2Cu2(Te4O11)](NO3)2 were grown under hydrothermal conditions. The crystal structures of all compounds comprise of characteristic coordination polyhedra, viz. nearly square [CuO4] plaquettes for divalent copper, octahedral [TeO6] units for hexavalent tellurium, trigonal-pyramidal [TeO3] and bisphenoidal [TeO4] groups for tetravalent tellurium, and distorted [PbOx] polyhedra for divalent lead. PbCuTeO5 is dimorphic and crystallizes in a monoclinic and a triclinic modification, related by a translationengleiche group-subgroup relation of index 2. PbCuTe2O6 represents the ideal composition of the rare mineral choloalite. The characteristic feature of the crystal structure of [Pb2Cu2(Te4O11)](NO3)2 is its layered set-up, comprised of cationic [Pb2Cu2(Te4O11)]2+ ribbons (width approximately 6.7 Å) sandwiched between nitrate anions that are only weakly bound to the cationic layers.