Mg3Er is alpha bismuth trifluoride structured and crystallizes in the cubic Fm-3m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a body-centered cubic geometry to four equivalent Mg(2) and four equivalent Er(1) atoms. In the second Mg site, Mg(2) is bonded in a distorted body-centered cubic geometry to eight equivalent Mg(1) and six equivalent Er(1) atoms. Er(1) is bonded in a distorted body-centered cubic geometry to six equivalent Mg(2) and eight equivalent Mg(1) atoms.
Mg3Er is alpha bismuth trifluoride structured and crystallizes in the cubic Fm-3m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a body-centered cubic geometry to four equivalent Mg(2) and four equivalent Er(1) atoms. All Mg(1)-Mg(2) bond lengths are 3.14 Å. All Mg(1)-Er(1) bond lengths are 3.14 Å. In the second Mg site, Mg(2) is bonded in a distorted body-centered cubic geometry to eight equivalent Mg(1) and six equivalent Er(1) atoms. All Mg(2)-Er(1) bond lengths are 3.63 Å. Er(1) is bonded in a distorted body-centered cubic geometry to six equivalent Mg(2) and eight equivalent Mg(1) atoms.