Tb4H9 crystallizes in the tetragonal I4/mmm space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a distorted body-centered cubic geometry to two equivalent H(2) and eight equivalent H(1) atoms. In the second Tb site, Tb(2) is bonded in a distorted body-centered cubic geometry to one H(2) and eight equivalent H(1) atoms. There are two inequivalent H sites. In the first H site, H(1) is bonded to two equivalent Tb(1) and two equivalent Tb(2) atoms to form HTb4 tetrahedra that share corners with three equivalent H(2)Tb6 octahedra, corners with sixteen equivalent H(1)Tb4 tetrahedra, edges with six equivalent H(1)Tb4 tetrahedra, and  a faceface with one H(2)Tb6 octahedra. The corner-sharing octahedral tilt angles range from 54-56°. In the second H site, H(2) is bonded to two equivalent Tb(2) and four equivalent Tb(1) atoms to form HTb6 octahedra that share corners with four equivalent H(2)Tb6 octahedra, corners with twenty-four equivalent H(1)Tb4 tetrahedra, and faces with eight equivalent H(1)Tb4 tetrahedra. The corner-sharing octahedra are not tilted.
Tb4H9 crystallizes in the tetragonal I4/mmm space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a distorted body-centered cubic geometry to two equivalent H(2) and eight equivalent H(1) atoms. Both Tb(1)-H(2) bond lengths are 2.60 Å. All Tb(1)-H(1) bond lengths are 2.27 Å. In the second Tb site, Tb(2) is bonded in a distorted body-centered cubic geometry to one H(2) and eight equivalent H(1) atoms. The Tb(2)-H(2) bond length is 2.59 Å. There are four shorter (2.21 Å) and four longer (2.27 Å) Tb(2)-H(1) bond lengths. There are two inequivalent H sites. In the first H site, H(1) is bonded to two equivalent Tb(1) and two equivalent Tb(2) atoms to form HTb4 tetrahedra that share corners with three equivalent H(2)Tb6 octahedra, corners with sixteen equivalent H(1)Tb4 tetrahedra, edges with six equivalent H(1)Tb4 tetrahedra, and  a faceface with one H(2)Tb6 octahedra. The corner-sharing octahedral tilt angles range from 54-56°. In the second H site, H(2) is bonded to two equivalent Tb(2) and four equivalent Tb(1) atoms to form HTb6 octahedra that share corners with four equivalent H(2)Tb6 octahedra, corners with twenty-four equivalent H(1)Tb4 tetrahedra, and faces with eight equivalent H(1)Tb4 tetrahedra. The corner-sharing octahedra are not tilted.