Noble gas compound
Noble gases can also make endohedral fullerene compounds when the noble gas atom is pushed inside a fullerene molecule. In 1993, it was discovered that when C60 is put under pressure of about 3 bar of Helium or Neon, He@C60 and Ne@C60 are made. Only about one out of every 650,000 C60 were found with a helium atom. But with more pressures (about 3000 bar), it is possible to get as much as 0.1%. Endohedral molecules with argon, krypton and xenon have also been made, as well as other compounds of He@C60.