Argon And Neon Form Novel Silicon Compounds

Noble-gas chemists have managed to snare two elusive compounds of the lighter elements argon and neon. Jana Roithová and Detlef Schröder of Charles University and the Czech Republic Academy of Sciences, both in Prague, used a mass spectrometry technique to make the gas-phase silicon-argon and silicon-neon molecules ArSiF₂ ²⁺ and NeSiF₂ ²⁺ (Angew. Chem. Int. Ed., DOI: 10.1002/anie.200903706). To form covalent bonds with the lighter inert noble gases requires extraordinary oxidizing agents. Thus, the researchers turned to the “superelectrophilic” dication SiF₃ ²⁺. Roithová and Schröder generated a stream of SiF₃ ²⁺ ions by ionizing SiF₄ in a mass spectrometer and then crashed them into argon atoms. They say the reaction can be thought of as a nucleophilic substitution, with argon displacing a fluorine to yield ArSiF₂ ²⁺. The team’s attempt to make the neon analog resulted in much lower yield. To date, there is only one known synthesized neutral argon compound (HArF), no neutral neon compounds, and few ionic compounds of either element, although scientists believe there should be some ionic species in interstellar space. The mass spectrometric identification of ArSiF₂ ²⁺ “raises hopes that eventually argon compounds could be isolated,” comments inorganic chemist Konrad Seppelt of the Free University of Berlin. “The work also shows that bonds to neon are very weak, so that presently their isolation seems hopeless.”