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HoB2 is hexagonal omega structure structured and crystallizes in the hexagonal P6/mmm space group. The structure is three-dimensional. Ho is bonded to twelve equivalent B atoms to form a mixture of edge and face-sharing HoB12 cuboctahedra. All Ho–B bond lengths are 2.70 Å. B is bonded in a 9-coordinate geometry to six equivalent Ho and three equivalent B atoms. All B–B bond lengths are 1.90 Å.
HoB4 crystallizes in the tetragonal P4/mbm space group. The structure is three-dimensional. Ho is bonded in a 4-coordinate geometry to eighteen B atoms. There are a spread of Ho–B bond distances ranging from 2.72–3.06 Å. There are three inequivalent B sites. In the first B site, B is bonded in a 1-coordinate geometry to four equivalent Ho and five B atoms. There is one shorter (1.63 Å) and four longer (1.75 Å) B–B bond length. In the second B site, B is bonded in a distorted trigonal planar geometry to six equivalent Ho and three B atoms. There is two shorter (1.71 Å) and one longer (1.74 Å) B–B bond length. In the third B site, B is bonded in a 9-coordinate geometry to four equivalent Ho and five B atoms. Both B–B bond lengths are 1.81 Å.
HoB6 is Calcium hexaboride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Ho is bonded in a 1-coordinate geometry to twenty-four equivalent B atoms. All Ho–B bond lengths are 3.00 Å. B is bonded in a 1-coordinate geometry to four equivalent Ho and five equivalent B atoms. There is one shorter (1.63 Å) and four longer (1.74 Å) B–B bond length.
HoB12 crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Ho is bonded in a 1-coordinate geometry to twenty-four equivalent B atoms. All Ho–B bond lengths are 2.78 Å. B is bonded in a 7-coordinate geometry to two equivalent Ho and five equivalent B atoms. There is one shorter (1.72 Å) and four longer (1.79 Å) B–B bond length.