Structural and thermochemical studies on Rb2TeCl6 and comparison with Rb2SnCl6

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Abstract
Using room temperature diffractometer intensity data the structure of Rb2TeCl6 has been determined by single crystal X-ray diffraction and refined to a final R of 0·050. The structure consists of regular octahedral [TeCl6]2–[Te–Cl = 2·541 Å(corrected)]. Lattice energy calculations on the resulting structure (for various charge distributions within the anion) are reported and are found to be sensitive to the assumed charge distributions within the anion. The measured heats of solution of TeCl4 and Rb2TeCl6 in hydrochloric acid allow the standard heat of formation of Rb2TeCl6 to be calculated as –294·4 kcal mol–1 at 298 K. Using the calculated lattice energy, the enthalpy of reaction (i) is calculated to be –21·8 ± 17 kcal mol–1 at 298 K where the large error in the value is a reflection of the uncertainties in the charge distribution of the anion. 2Cl–(g)+ TeCl4(g)→[TeCl6]2–(g)(i) Thermochemical measurements on the analogous tin compounds gives the standard heat of formation of Rb2SnCl6 as –365·5 kcal mol–1 at 298 K, and, together with the lattice energy calculations, allow the enthalpy change for reaction (ii) to be estimated. 2Cl–(g)+ SnCl4(g)→[SnCl6]2–(g)(ii) As measured by the enthalpy of the gas phase reaction, the two Lewis acids SnCl4 and TeCl4 have, towards the chloride ion ligand, the same acceptor strength.

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