Hf5N5O2 crystallizes in the monoclinic C2/m space group. There are three inequivalent Hf sites. In the first Hf site, Hf(1) is bonded to two equivalent N(1), three equivalent N(3), and one O(1) atom to form HfN5O octahedra that share  a cornercorner with one Hf(3)N4O2 octahedra, corners with two equivalent Hf(1)N5O octahedra, and edges with five equivalent Hf(1)N5O octahedra. The corner-sharing octahedral tilt angles range from 0-60°. In the second Hf site, Hf(2) is bonded in a 7-coordinate geometry to two equivalent N(3), three equivalent N(2), and two equivalent O(1) atoms. In the third Hf site, Hf(3) is bonded to four equivalent N(2) and two equivalent O(1) atoms to form HfN4O2 octahedra that share corners with two equivalent Hf(1)N5O octahedra and edges with two equivalent Hf(3)N4O2 octahedra. The corner-sharing octahedral tilt angles are 60°. There are three inequivalent N sites. In the first N site, N(1) is bonded in a square co-planar geometry to four equivalent Hf(1) atoms. In the second N site, N(2) is bonded to two equivalent Hf(3) and three equivalent Hf(2) atoms to form distorted NHf5 trigonal bipyramids that share corners with four equivalent O(1)Hf4 tetrahedra, corners with two equivalent N(2)Hf5 trigonal bipyramids, corners with four equivalent N(3)Hf5 trigonal bipyramids, edges with three equivalent O(1)Hf4 tetrahedra,  an edgeedge with one N(3)Hf5 trigonal bipyramid, and edges with five equivalent N(2)Hf5 trigonal bipyramids. In the third N site, N(3) is bonded to two equivalent Hf(2) and three equivalent Hf(1) atoms to form NHf5 trigonal bipyramids that share corners with five equivalent O(1)Hf4 tetrahedra, corners with four equivalent N(2)Hf5 trigonal bipyramids,  an edgeedge with one O(1)Hf4 tetrahedra,  an edgeedge with one N(2)Hf5 trigonal bipyramid, and edges with four equivalent N(3)Hf5 trigonal bipyramids. O(1) is bonded to one Hf(1), one Hf(3), and two equivalent Hf(2) atoms to form OHf4 tetrahedra that share corners with three equivalent O(1)Hf4 tetrahedra, corners with four equivalent N(2)Hf5 trigonal bipyramids, corners with five equivalent N(3)Hf5 trigonal bipyramids,  an edgeedge with one N(3)Hf5 trigonal bipyramid, and edges with three equivalent N(2)Hf5 trigonal bipyramids.
Hf5N5O2 crystallizes in the monoclinic C2/m space group. There are three inequivalent Hf sites. In the first Hf site, Hf(1) is bonded to two equivalent N(1), three equivalent N(3), and one O(1) atom to form HfN5O octahedra that share  a cornercorner with one Hf(3)N4O2 octahedra, corners with two equivalent Hf(1)N5O octahedra, and edges with five equivalent Hf(1)N5O octahedra. The corner-sharing octahedral tilt angles range from 0-60°. Both Hf(1)-N(1) bond lengths are 2.17 Å. There is one shorter (2.21 Å) and two longer (2.22 Å) Hf(1)-N(3) bond lengths. The Hf(1)-O(1) bond length is 2.18 Å. In the second Hf site, Hf(2) is bonded in a 7-coordinate geometry to two equivalent N(3), three equivalent N(2), and two equivalent O(1) atoms. Both Hf(2)-N(3) bond lengths are 2.30 Å. There are two shorter (2.28 Å) and one longer (2.41 Å) Hf(2)-N(2) bond length. Both Hf(2)-O(1) bond lengths are 2.22 Å. In the third Hf site, Hf(3) is bonded to four equivalent N(2) and two equivalent O(1) atoms to form HfN4O2 octahedra that share corners with two equivalent Hf(1)N5O octahedra and edges with two equivalent Hf(3)N4O2 octahedra. The corner-sharing octahedral tilt angles are 60°. All Hf(3)-N(2) bond lengths are 2.19 Å. Both Hf(3)-O(1) bond lengths are 2.11 Å. There are three inequivalent N sites. In the first N site, N(1) is bonded in a square co-planar geometry to four equivalent Hf(1) atoms. In the second N site, N(2) is bonded to two equivalent Hf(3) and three equivalent Hf(2) atoms to form distorted NHf5 trigonal bipyramids that share corners with four equivalent O(1)Hf4 tetrahedra, corners with two equivalent N(2)Hf5 trigonal bipyramids, corners with four equivalent N(3)Hf5 trigonal bipyramids, edges with three equivalent O(1)Hf4 tetrahedra,  an edgeedge with one N(3)Hf5 trigonal bipyramid, and edges with five equivalent N(2)Hf5 trigonal bipyramids. In the third N site, N(3) is bonded to two equivalent Hf(2) and three equivalent Hf(1) atoms to form NHf5 trigonal bipyramids that share corners with five equivalent O(1)Hf4 tetrahedra, corners with four equivalent N(2)Hf5 trigonal bipyramids,  an edgeedge with one O(1)Hf4 tetrahedra,  an edgeedge with one N(2)Hf5 trigonal bipyramid, and edges with four equivalent N(3)Hf5 trigonal bipyramids. O(1) is bonded to one Hf(1), one Hf(3), and two equivalent Hf(2) atoms to form OHf4 tetrahedra that share corners with three equivalent O(1)Hf4 tetrahedra, corners with four equivalent N(2)Hf5 trigonal bipyramids, corners with five equivalent N(3)Hf5 trigonal bipyramids,  an edgeedge with one N(3)Hf5 trigonal bipyramid, and edges with three equivalent N(2)Hf5 trigonal bipyramids.