ErNi7B3 crystallizes in the tetragonal I4_1/amd space group. Er(1) is bonded in a 18-coordinate geometry to two equivalent Ni(4), four equivalent Ni(1), four equivalent Ni(2), four equivalent Ni(3), and four equivalent B(1) atoms. There are four inequivalent Ni sites. In the first Ni site, Ni(1) is bonded in a 6-coordinate geometry to two equivalent Er(1), two equivalent B(1), and two equivalent B(2) atoms. In the second Ni site, Ni(2) is bonded in a 5-coordinate geometry to two equivalent Er(1), one B(2), and two equivalent B(1) atoms. In the third Ni site, Ni(3) is bonded in a 3-coordinate geometry to two equivalent Er(1) and two equivalent B(1) atoms. In the fourth Ni site, Ni(4) is bonded in a distorted square co-planar geometry to two equivalent Er(1), two equivalent B(1), and two equivalent B(2) atoms. There are two inequivalent B sites. In the first B site, B(1) is bonded in a 7-coordinate geometry to two equivalent Er(1), one Ni(4), two equivalent Ni(1), two equivalent Ni(2), and two equivalent Ni(3) atoms. In the second B site, B(2) is bonded in a 9-coordinate geometry to two equivalent Ni(2), two equivalent Ni(4), four equivalent Ni(1), and one B(2) atom.
ErNi7B3 crystallizes in the tetragonal I4_1/amd space group. Er(1) is bonded in a 18-coordinate geometry to two equivalent Ni(4), four equivalent Ni(1), four equivalent Ni(2), four equivalent Ni(3), and four equivalent B(1) atoms. Both Er(1)-Ni(4) bond lengths are 3.13 Å. All Er(1)-Ni(1) bond lengths are 2.83 Å. There are two shorter (2.72 Å) and two longer (2.78 Å) Er(1)-Ni(2) bond lengths. There are two shorter (2.60 Å) and two longer (2.77 Å) Er(1)-Ni(3) bond lengths. All Er(1)-B(1) bond lengths are 2.86 Å. There are four inequivalent Ni sites. In the first Ni site, Ni(1) is bonded in a 6-coordinate geometry to two equivalent Er(1), two equivalent B(1), and two equivalent B(2) atoms. Both Ni(1)-B(1) bond lengths are 2.15 Å. Both Ni(1)-B(2) bond lengths are 2.22 Å. In the second Ni site, Ni(2) is bonded in a 5-coordinate geometry to two equivalent Er(1), one B(2), and two equivalent B(1) atoms. The Ni(2)-B(2) bond length is 2.09 Å. Both Ni(2)-B(1) bond lengths are 2.02 Å. In the third Ni site, Ni(3) is bonded in a 3-coordinate geometry to two equivalent Er(1) and two equivalent B(1) atoms. Both Ni(3)-B(1) bond lengths are 2.04 Å. In the fourth Ni site, Ni(4) is bonded in a distorted square co-planar geometry to two equivalent Er(1), two equivalent B(1), and two equivalent B(2) atoms. Both Ni(4)-B(1) bond lengths are 2.21 Å. Both Ni(4)-B(2) bond lengths are 2.17 Å. There are two inequivalent B sites. In the first B site, B(1) is bonded in a 7-coordinate geometry to two equivalent Er(1), one Ni(4), two equivalent Ni(1), two equivalent Ni(2), and two equivalent Ni(3) atoms. In the second B site, B(2) is bonded in a 9-coordinate geometry to two equivalent Ni(2), two equivalent Ni(4), four equivalent Ni(1), and one B(2) atom. The B(2)-B(2) bond length is 1.82 Å.