 4 ) , both of which are dangerously explosive and powerful oxidizing agents , and xenon dioxide ( <unk> ) , which was reported in 2011 with a coordination number of four . <unk> forms when xenon <unk> is poured over ice . Its crystal structure may allow it to replace silicon in <unk> minerals . The <unk> + cation has been identified by infrared spectroscopy in solid argon . 
