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BY-NC-ND 3.0 license Open Access Published by De Gruyter June 2, 2014

Polymorphie von Tellur(IV)-iodid/ Polymorphism of Tellurium(IV) Iodide

  • Rüdiger Kniep , Heinz Jürgen Beister and Dieter Wald

Abstract

Idiomorphous crystals of five different polymorphic modifications (α-ε) of TeI4 are simultaneously grown from solutions of TeI4 and concentrated HI in methanol by evaporating the solvent at room temperature. δ-TeI4 is the only stable phase at normal conditions. Phase transformations of α-, β-, γ-and ε-TeI4 to the final stage δ-TeI4 take place by heating and run through discrete intermediates. The observed graduations lead to a sequence γ-, β-, α-,ε-TeI4 which indicates “increasing metastability”. The crystal structures of α-TeI4 (trigonal; P3̄ml; a = 4.228(2), c - 6.684(6)Å, Z = 0.5; Dx = 5.10 g/cm 3), β-TeI4 (orthorhombic; Pn21m; a = 6.888(2), b = 14.539(3), c = 16.753(4) Å, Z = 8; Dx = 5.03 g/cm3) and γ-TeI4 (monoclinic; P21/c; a = 11.199(4), b = 13.599(4), c = 22.158(6) Å,β = 98.10(3)°, Z = 16; D, = 5.05 g/cm3) are related to the known crystal structure of δ-TeI4. α-TeI4 (“Te0.5I2”) is an isotype of the 2H-CdI : structure with random distribution of Te over the Cd-positions. The crystal structures of β-, γ-and δ-TeI 4 contain discrete tetrameric molecules “(TeI4)2 (TeI3+I-)2” which are generated by ordered distributions of Te over 1/4 of the octahedral holes of a 2H-(β) and a 4H-sequence (y,δ ) of the nearly close packed iodine layers. A nearly cubic close packing of Iodine atoms is observed in the crystal structure of ε-TeI4 (tetragonal; I41/amd; a = 16.875(6), c -11.829(5) Å, Z = 16; Dx = 5.01 g/cm 3). The ordered distribution of Te in 1/4 of the octahedral holes leads to tetrameric molecules “(TeI3+I-)4” in a cubanelike arrangement which, thus far, has been observed only in the crystal structures of TeCl4 and TeBr4 . The Madelung Parts of Lattice Energies, MAPLE, of β-, γ-, δ-and ε-TeI4 are calculated.

Received: 1988-4-11
Published Online: 2014-6-2
Published in Print: 1988-8-1

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