Neil Bartlett initially carried out a reaction between oxygen and PtF6. This resulted in the formation of a red compound, O+2 [Pt F6 ].
Later he realised that the first ionization energy of oxygen (1175 kJ/mol) and Xe (1170 kJ/mol) is almost the same. Thus, he tried to prepare a compound with Xe and PtF6. He was successful and a red coloured compound, Xe+ [PtF6]- was formed.