& Xenon Ultraviolet Photolysis Studies on XeO 4 in Noble-Gas and F 2 Matrices and the Formation and Characterization of a New Xe VIII Oxide, (h 2 -O 2 )XeO 3 Thomas Vent-Schmidt, [a] James T. Goettel, [c] Gary J. Schrobilgen ,* [a, c] and Sebastian Riedel* [b] Abstract: The photolytic behavior of the thermochemically unstable xenon(VIII) oxide XeO 4 was investigated by UV irra- diation in noble-gas and F 2 matrices. Photolysis of Xe 16 O 4 or Xe 18 O 4 in noble-gas matrices at 365 nm yielded XeO 3 and a new xenon(VIII) oxide, namely, (h 2 -O 2 )XeO 3 , which, along with XeO 4 , was characterized by matrix-isolation IR spectros- copy and quantum-chemical calculations. Calculations of the UV spectrum showed that the photodecomposition is in- duced by an n !s* transition, but the nature of the excita- tion differs when different light sources are used. There is strong evidence for the formation of mobile 1 D excited O atoms in the case of excitation at 365 nm, which led to the formation of (h 2 -O 2 )XeO 3 by reaction with XeO 4 . Matrix-isola- tion IR spectroscopy in Ne and Ar matrices afforded the nat- ural-abundance xenon isotopic pattern for the n 3 (T 2 ) stretch- ing mode of Xe 16 O 4 , and 18 O enrichment provided the 16 O/ 18 O isotopic shifts of XeO 4 and (h 2 -O 2 )XeO 3 . Introduction Xenon forms three binary oxides, XeO 2 (s), XeO 3 (s), and XeO 4 (g), which are solids and a gas at room temperature. All three oxides are thermodynamically unstable and shock-sensitive. Xenon trioxide and XeO 4 decompose explosively to their ele- ments with the release of 402 [1] and 642 kJ mol 1 , [2] respectively, whereas water-insoluble XeO 2 decomposes at 0 8C over several minutes to Xe and O 2 . [3] Despite their hazardous natures, the molecular structures of XeO 3 and XeO 4 have been obtained from a single-crystal X-ray diffraction study on XeO 3 [4] and an electron diffraction study on gaseous XeO 4 . [5] Vibrational fre- quencies for XeO 4 have been previously obtained by gas- phase IR spectroscopy [6] and by Raman spectroscopy in the solid state [7] and in anhydrous HF. [8] Until recently, ruthenium, osmium, and xenon were the only elements in the periodic table to display the highest oxidation state that was then attainable, + 8. More recently, examples of Ir VIII , in IrO 4 , [9] and Ir IX , in [IrO 4 ] + , [10] have been reported. Iridium tetroxide was characterized at low temperature by matrix-isola- tion IR spectroscopy, whereas the [IrO 4 ] + cation was character- ized in the gas phase by IR photodissociation spectroscopy and mass spectrometry. Vibrational characterization was aided by 16/18 O isotopic splittings observed in their IR absorption bands. In recent years, considerable progress has been made in extending and understanding the oxide fluoride chemistry of Os VIII . [11–15] This chemistry is wholly reliant on OsO 4 , the stable synthetic precursor for all Os VIII oxide fluoride com- pounds. The shock-sensitive and treacherous nature of XeO 4 has no doubt impeded progress in Xe VIII chemistry, which has pro- gressed little beyond the synthesis and structural characteriza- tion of the remarkably stable perxenate anion, [XeO 6 ] 4 , [16–19] and the work by Huston and co-workers, [6, 20] who first synthe- sized and structurally characterized XeO 4 . [5–7] Huston and co- workers [21] also demonstrated the existence of the only other Xe VIII compounds that are presently known, namely, XeO 3 F 2 , which was characterized by matrix-isolation IR and Raman spectroscopy, and XeO 2 F 4 , [22] which has only been characterized in the gas phase by mass spectrometry. Both oxide fluorides were derived from XeO 4 by oxygen–fluorine metathesis with XeF 6 . The 19 F and 129 Xe NMR spectra of XeO 3 F 2 have been re- ported in a more recent study. [23] A more detailed procedure for the preparation of XeO 4 has been reported by Gerken and Schrobilgen, [8] who also described the preparation of solution samples of XeO 4 in SO 2 ClF, BrF 5 , and HF. This work led to the stabilization of XeO 4 in the aforementioned oxidatively resist- ant and synthetically useful solvent media, and to the charac- terization of XeO 4 for the first time in solution (anhydrous HF), by 129 Xe, 131 Xe, and 17 O NMR and Raman spectroscopy. This study established that synthetically useful XeO 4 solutions could be prepared that have sufficient kinetic stability and the poten- tial to further extend Xe VIII chemistry. [a] T. Vent-Schmidt, Prof. Dr. G. J. Schrobilgen Albert-Ludwigs Universität Freiburg Institut für Anorganische und Analytische Chemie Albertstrasse 21, 79104 Freiburg (Germany) [b] Prof. Dr. S. Riedel Freie Universität Berlin, Institut für Chemie und Biochemie Fabeckstrasse 34–36, 14195 Berlin (Germany) E-mail : s.riedel@fu-berlin.de [c] J. T. Goettel, Prof. Dr. G. J. Schrobilgen McMaster University, Department of Chemistry 1280 Main Street West, Hamilton, Ontario L8S 4M1 (Canada) E-mail : schrobil@mcmaster.ca Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201500964. Chem. Eur. J. 2015, 21, 11244 – 11252 # 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 11244 Full Paper DOI: 10.1002/chem.201500964