Copper deficiency in UCu~5{-~ x }Sn [ x = 0.37(1)]

The ternary inter­metallic title compound, known hitherto as UCu5Sn (uranium penta­copper stannide), crystallizes with the hexa­gonal CeNi5Sn structure type, and it has been presumed to be a fully stoichiometric phase, devoid of any disorder. However, the present single-crystal X-ray diffraction studies at 120 K, carried out with crystals grown from an Sn flux, suggest the existence of a previously unnoticed phase width of the title compound UCu5−xSn. All the atoms occupy special positions: U (\overline{6}m2, \overline{3}m.), Sn (3m.) and Cu (.m., 3m., and two positions with \overline{6}m2).