  The pyrochlore oxide Pb2Re2O7-{\delta} (PRO) is a candidate
spin-orbit-coupled metal (SOCM) that exhibits a structural phase transition
with inversion symmetry breaking. In this study, we report the results of
detailed X-ray diffraction (XRD) measurements on single crystals of PRO to
clarify the crystal structure below the phase transition temperature at Ts =
300 K. In the XRD patterns, a clear peak splitting is observed below Ts,
indicating a cubic to tetragonal transition. Based on the group-subgroup
relationship and the observed reflection conditions, the space group of the
low-temperature phase is proposed to be I4122, which agrees with optical second
harmonic generation measurements. This space group is the same as that of the
lowest temperature structure of the analogous SOCM Cd2Re2O7 (CRO), which is
realized by the emergence of odd-parity multipole order. The comparison between
PRO and CRO allows for advancing our understanding on the symmetry-lowering
complex order exhibited by SOCMs.
