Crystal structures of trimethylammonium hexaiodotellurate(IV) and heptaiodotellurate(IV).

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Crystal structures of the title compounds were determined by X-ray diffraction method. The crystal data and the final R values are: [(CH3)3NH]2TeI6, cubic, Pa3, a=13.210(2) Å, V=2305.2(9) Å3, Z=4, R=0.057 for 263 observed unique reflections and [(CH3)3NH]2TeI7, tetragonal, P4⁄nmm, a=13.921(3), c=6.224(2) Å, V=1206.4(8) Å3, Z=2, R=0.051 for 553 reflections. The structure of hexaiodo complex is a modified K2PtCl6 type. The discrete[TeI6]2− octahedra are practically regular with a Te–I distance of 2.952(2) Å. The trimethylammonium cations lie on the unit cell triad axes and form trifurcated, weak hydrogen bonds of NH···3I. In contrast, the TeIV coordination in the heptaiodo complex is an elongated octahedron with Te–I(1)=2.934(1) and Te–I(2)=3.124(4), 3.100(4) Å. These TeI6 octahedra form linear trans TeI5 chains running along c by sharing each pair of opposite vertices. Extra iodine atoms also stack along c with nearly equidistant I–I separations of 3.091(6) and 3.133(6) Å. The trimethylammonium cation is distributed randomly over four configurations in a cavity formed by two [TeI5]nn− and two [I]2nn− columns. Thus, the chemical constitution of the heptaiodo complex can be expressed as di-trimethylammonium catena-μ-iodo-tetraiodo tellurate(1-) catena-diiodide(1-), [(CH3)3NH]2n2n+[TeI5]nn−[I]2nn−.
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