ErNi4B crystallizes in the hexagonal P6/mmm space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 18-coordinate geometry to twelve equivalent Ni(2) and six equivalent B(1) atoms. In the second Er site, Er(2) is bonded in a distorted hexagonal planar geometry to six equivalent Ni(1) atoms. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded in a 12-coordinate geometry to three equivalent Er(2), three equivalent Ni(1), and six equivalent Ni(2) atoms. In the second Ni site, Ni(2) is bonded in a distorted L-shaped geometry to two equivalent Er(1), two equivalent Ni(1), and two equivalent B(1) atoms. B(1) is bonded in a 6-coordinate geometry to three equivalent Er(1) and six equivalent Ni(2) atoms.
ErNi4B crystallizes in the hexagonal P6/mmm space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 18-coordinate geometry to twelve equivalent Ni(2) and six equivalent B(1) atoms. All Er(1)-Ni(2) bond lengths are 2.84 Å. All Er(1)-B(1) bond lengths are 2.83 Å. In the second Er site, Er(2) is bonded in a distorted hexagonal planar geometry to six equivalent Ni(1) atoms. All Er(2)-Ni(1) bond lengths are 2.83 Å. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded in a 12-coordinate geometry to three equivalent Er(2), three equivalent Ni(1), and six equivalent Ni(2) atoms. All Ni(1)-Ni(1) bond lengths are 2.83 Å. All Ni(1)-Ni(2) bond lengths are 2.45 Å. In the second Ni site, Ni(2) is bonded in a distorted L-shaped geometry to two equivalent Er(1), two equivalent Ni(1), and two equivalent B(1) atoms. Both Ni(2)-B(1) bond lengths are 2.02 Å. B(1) is bonded in a 6-coordinate geometry to three equivalent Er(1) and six equivalent Ni(2) atoms.