Peroxide Coordination of Tellurium in Aqueous Solutions.

Abstract

Tellurium-peroxo complexes in aqueous solutions have never been reported. In this work, ammonium peroxotellurates (NH4 )4 Te2 (μ-OO)2 (μ-O)O4 (OH)2 (1) and (NH4 )5 Te2 (μ-OO)2 (μ-O)O5 (OH)⋅1.28 H2 O⋅0.72 H2 O2 (2) were isolated from 5 % hydrogen peroxide aqueous solutions of ammonium tellurate and characterized by single-crystal and powder X-ray diffraction analysis, by Raman spectroscopy and thermal analysis. The crystal structure of 1 comprises ammonium cations and a symmetric binuclear peroxotellurate anion [Te2 (μ-OO)2 (μ-O)O4 (OH)2 ](4-) . The structure of 2 consists of an unsymmetrical [Te2 (μ-OO)2 (μ-O)O5 (OH)](5-) anion, ammonium cations, hydrogen peroxide, and water. Peroxotellurate anions in both 1 and 2 contain a binuclear Te2 (μ-OO)2 (μ-O) fragment with one μ-oxo- and two μ-peroxo bridging groups. (125) Te NMR spectroscopic analysis shows that the peroxo bridged bitellurate anions are the dominant species in solution, with 3-40 %wt H2 O2 and for pH values above 9. DFT calculations of the peroxotellurate anion confirm its higher thermodynamic stability compared with those of the oxotellurate analogues. This is the first direct evidence for tellurium-peroxide coordination in any aqueous system and the first report of inorganic tellurium-peroxo complexes. General features common to all reported p-block element peroxides could be discerned by the characterization of aqueous and crystalline peroxotellurates.