La5Si3 crystallizes in the tetragonal I4/mcm space group. There are two inequivalent La sites. In the first La site, La(1) is bonded in a 5-coordinate geometry to two equivalent Si(2) and three equivalent Si(1) atoms. In the second La site, La(2) is bonded to two equivalent Si(2) and four equivalent Si(1) atoms to form distorted corner-sharing LaSi6 octahedra. The corner-sharing octahedral tilt angles range from 0-58°. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to two equivalent La(2), six equivalent La(1), and one Si(1) atom. In the second Si site, Si(2) is bonded in a 10-coordinate geometry to two equivalent La(2) and eight equivalent La(1) atoms.
La5Si3 crystallizes in the tetragonal I4/mcm space group. There are two inequivalent La sites. In the first La site, La(1) is bonded in a 5-coordinate geometry to two equivalent Si(2) and three equivalent Si(1) atoms. Both La(1)-Si(2) bond lengths are 3.28 Å. There is one shorter (3.15 Å) and two longer (3.16 Å) La(1)-Si(1) bond lengths. In the second La site, La(2) is bonded to two equivalent Si(2) and four equivalent Si(1) atoms to form distorted corner-sharing LaSi6 octahedra. The corner-sharing octahedral tilt angles range from 0-58°. Both La(2)-Si(2) bond lengths are 3.50 Å. All La(2)-Si(1) bond lengths are 3.24 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to two equivalent La(2), six equivalent La(1), and one Si(1) atom. The Si(1)-Si(1) bond length is 2.55 Å. In the second Si site, Si(2) is bonded in a 10-coordinate geometry to two equivalent La(2) and eight equivalent La(1) atoms.