HoO crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ho is bonded to five equivalent O atoms to form a mixture of edge and corner-sharing HoO5 trigonal bipyramids. There are three shorter (2.29 Å) and two longer (2.41 Å) Ho–O bond lengths. O is bonded to five equivalent Ho atoms to form a mixture of edge and corner-sharing OHo5 trigonal bipyramids.