TbAl2Si2 crystallizes in the trigonal P-3m1 space group. Tb(1) is bonded to six equivalent Si(1) atoms to form distorted TbSi6 octahedra that share corners with twelve equivalent Al(1)Si4 tetrahedra, edges with six equivalent Tb(1)Si6 octahedra, and edges with six equivalent Al(1)Si4 tetrahedra. Al(1) is bonded to four equivalent Si(1) atoms to form distorted AlSi4 tetrahedra that share corners with six equivalent Tb(1)Si6 octahedra, corners with six equivalent Al(1)Si4 tetrahedra, edges with three equivalent Tb(1)Si6 octahedra, and edges with three equivalent Al(1)Si4 tetrahedra. The corner-sharing octahedral tilt angles range from 21-54°. Si(1) is bonded to three equivalent Tb(1) and four equivalent Al(1) atoms to form a mixture of distorted corner and edge-sharing SiTb3Al4 pentagonal bipyramids.
TbAl2Si2 crystallizes in the trigonal P-3m1 space group. Tb(1) is bonded to six equivalent Si(1) atoms to form distorted TbSi6 octahedra that share corners with twelve equivalent Al(1)Si4 tetrahedra, edges with six equivalent Tb(1)Si6 octahedra, and edges with six equivalent Al(1)Si4 tetrahedra. All Tb(1)-Si(1) bond lengths are 2.97 Å. Al(1) is bonded to four equivalent Si(1) atoms to form distorted AlSi4 tetrahedra that share corners with six equivalent Tb(1)Si6 octahedra, corners with six equivalent Al(1)Si4 tetrahedra, edges with three equivalent Tb(1)Si6 octahedra, and edges with three equivalent Al(1)Si4 tetrahedra. The corner-sharing octahedral tilt angles range from 21-54°. There are three shorter (2.49 Å) and one longer (2.52 Å) Al(1)-Si(1) bond length. Si(1) is bonded to three equivalent Tb(1) and four equivalent Al(1) atoms to form a mixture of distorted corner and edge-sharing SiTb3Al4 pentagonal bipyramids.