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Reactions with Oleum under Harsh Conditions: Characterization of the Unique [M(S2O7)3]2− Ions (M=Si, Ge, Sn) in A2[M(S2O7)3] (A=NH4, Ag)

Authors

  • Christian Logemann,

    1. Carl von Ossietzky University of Oldenburg, Institute of Pure and Applied Chemistry, Carl-von-Ossietzky-Strasse 9-11, 26129 Oldenburg (Germany), Fax: (+49) 441-798-3352
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  • Daniel Gunzelmann,

    1. University of Bayreuth, Chair of Inorganic Chemistry III, Universitätsstr. 30, 95447 Bayreuth (Germany)
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  • Prof. Dr. Thorsten Klüner,

    1. Carl von Ossietzky University of Oldenburg, Institute of Pure and Applied Chemistry, Carl-von-Ossietzky-Strasse 9-11, 26129 Oldenburg (Germany), Fax: (+49) 441-798-3352
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  • Prof. Dr. Jürgen Senker,

    1. University of Bayreuth, Chair of Inorganic Chemistry III, Universitätsstr. 30, 95447 Bayreuth (Germany)
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  • Prof. Dr. Mathias S. Wickleder

    Corresponding author
    1. Carl von Ossietzky University of Oldenburg, Institute of Pure and Applied Chemistry, Carl-von-Ossietzky-Strasse 9-11, 26129 Oldenburg (Germany), Fax: (+49) 441-798-3352
    • Carl von Ossietzky University of Oldenburg, Institute of Pure and Applied Chemistry, Carl-von-Ossietzky-Strasse 9-11, 26129 Oldenburg (Germany), Fax: (+49) 441-798-3352
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Abstract

The reactions of group 14 tetrachlorides MCl4 (M=Si, Ge, Sn) with oleum (65 % SO3) at elevated temperatures lead to the unique complex ions [M(S2O7)3]2−, which show the central M atoms in coordination with three chelating S2O72− groups. The mean distances M[BOND]O within the anions increase from 175.6(2)–177.5(2) pm (M=Si) to 186.4(4)–187.7(4) pm (M=Ge) to 201.9(2)–203.5(2) pm (M=Sn). These distances are reproduced well by DFT calculations. The same calculations show an increasing positive charge for the central M atom in the row Si, Ge, Sn, which can be interpreted as the decreasing covalency of the M[BOND]O bonds. For the silicon compound (NH4)2[Si(S2O7)3], 29Si solid-state NMR measurements have been performed, with the results showing a signal at −215.5 ppm for (NH4)2[Si(S2O7)3], which is in very good agreement with theoretical estimations. In addition, the vibrational modes within the [MO6] skeleton have been monitored by Raman spectroscopy for selected examples, and are well reproduced by theory. The charge balance for the [M(S2O7)3]2− ions is achieved by monovalent A+ counter ions (A=NH4, Ag), which are implemented in the syntheses in the form of their sulfates. The sizes of the A+ ions, that is, their coordination requirements, cause the crystallographic differences in the crystal structures, although the complex [M(S2O7)3]2− ions remain essentially unaffected with the different A+ ions. Furthermore, the nature of the A+ ions influences the thermal behavior of the compounds, which has been monitored for selected examples by thermogravimetric differential thermal analysis (DTA/TG) and XRD measurements.

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