Er5BSi3 crystallizes in the hexagonal P6_3/mcm space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 7-coordinate geometry to two equivalent B(1) and five equivalent Si(1) atoms. In the second Er site, Er(2) is bonded in a 6-coordinate geometry to six equivalent Si(1) atoms. B(1) is bonded to six equivalent Er(1) atoms to form face-sharing BEr6 octahedra. Si(1) is bonded in a 9-coordinate geometry to four equivalent Er(2) and five equivalent Er(1) atoms.
Er5BSi3 crystallizes in the hexagonal P6_3/mcm space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 7-coordinate geometry to two equivalent B(1) and five equivalent Si(1) atoms. Both Er(1)-B(1) bond lengths are 2.57 Å. There are a spread of Er(1)-Si(1) bond distances ranging from 2.94-3.41 Å. In the second Er site, Er(2) is bonded in a 6-coordinate geometry to six equivalent Si(1) atoms. All Er(2)-Si(1) bond lengths are 3.02 Å. B(1) is bonded to six equivalent Er(1) atoms to form face-sharing BEr6 octahedra. Si(1) is bonded in a 9-coordinate geometry to four equivalent Er(2) and five equivalent Er(1) atoms.