  Although Xe is known to form stable compounds with strong electronegative
elements, evidence on the formation of stable compounds with electropositive
elements, such as Fe and Ni, was missing until very recently. In addition to
the significance of the emerging field of noble gas elements chemistry, the
possible formation of Xe-Fe/Ni compounds has been proposed as a plausible
explanation of the so-called "missing Xe paradox". Here we explore the possible
formation of stable compounds in the Xe-Fe/Ni systems at thermodynamic
conditions representative of Earth's core. Using in situ synchrotron X-ray
diffraction and Raman spectroscopy in concert with first principles
calculations we demonstrate the synthesis of stable Xe(Fe,Fe/Ni)$_3$ and
XeNi$_3$ compounds. The results indicate the changing chemical properties of
elements under extreme conditions where noble gas elements can form stable
compounds with elements which are electropositive at ambient conditions but
become slightly electronegative at high pressures.
