Eu3(MgSi)5 crystallizes in the orthorhombic Pnma space group. There are five inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one Si(4) and three equivalent Si(1) atoms to form MgSi4 tetrahedra that share  a cornercorner with one Mg(4)Eu2Si4 tetrahedra,  a cornercorner with one Mg(5)Eu2Si4 tetrahedra,  a cornercorner with one Mg(2)EuSi4 tetrahedra, corners with two equivalent Mg(1)Si4 tetrahedra, edges with two equivalent Mg(2)EuSi4 tetrahedra, and edges with two equivalent Mg(1)Si4 tetrahedra. In the second Mg site, Mg(2) is bonded to one Eu(3), one Si(1), one Si(2), and two equivalent Si(4) atoms to form distorted MgEuSi4 tetrahedra that share  a cornercorner with one Mg(1)Si4 tetrahedra, corners with two equivalent Mg(4)Eu2Si4 tetrahedra, corners with two equivalent Mg(2)EuSi4 tetrahedra, corners with two equivalent Mg(3)EuSi4 tetrahedra, edges with two equivalent Mg(4)Eu2Si4 tetrahedra, edges with two equivalent Mg(1)Si4 tetrahedra, and faces with two equivalent Mg(5)Eu2Si4 tetrahedra. In the third Mg site, Mg(3) is bonded to one Eu(3), one Si(2), and three equivalent Si(5) atoms to form distorted MgEuSi4 tetrahedra that share  a cornercorner with one Mg(4)Eu2Si4 tetrahedra, corners with two equivalent Mg(2)EuSi4 tetrahedra, corners with two equivalent Mg(3)EuSi4 tetrahedra, corners with four equivalent Mg(5)Eu2Si4 tetrahedra, edges with two equivalent Mg(3)EuSi4 tetrahedra, and faces with two equivalent Mg(4)Eu2Si4 tetrahedra. In the fourth Mg site, Mg(4) is bonded to two equivalent Eu(3), one Si(4), one Si(5), and two equivalent Si(2) atoms to form distorted MgEu2Si4 tetrahedra that share  a cornercorner with one Mg(3)EuSi4 tetrahedra,  a cornercorner with one Mg(1)Si4 tetrahedra, corners with two equivalent Mg(2)EuSi4 tetrahedra, corners with four equivalent Mg(5)Eu2Si4 tetrahedra,  an edgeedge with one Mg(5)Eu2Si4 tetrahedra, edges with two equivalent Mg(4)Eu2Si4 tetrahedra, edges with two equivalent Mg(2)EuSi4 tetrahedra,  a faceface with one Mg(5)Eu2Si4 tetrahedra, and faces with two equivalent Mg(3)EuSi4 tetrahedra. In the fifth Mg site, Mg(5) is bonded to two equivalent Eu(3), one Si(3), one Si(4), and two equivalent Si(2) atoms to form distorted MgEu2Si4 tetrahedra that share  a cornercorner with one Mg(1)Si4 tetrahedra, corners with four equivalent Mg(4)Eu2Si4 tetrahedra, corners with four equivalent Mg(3)EuSi4 tetrahedra,  an edgeedge with one Mg(4)Eu2Si4 tetrahedra, edges with two equivalent Mg(5)Eu2Si4 tetrahedra,  a faceface with one Mg(4)Eu2Si4 tetrahedra, and faces with two equivalent Mg(2)EuSi4 tetrahedra. There are three inequivalent Eu sites. In the first Eu site, Eu(1) is bonded in a 7-coordinate geometry to one Si(2), two equivalent Si(1), two equivalent Si(3), and two equivalent Si(4) atoms. In the second Eu site, Eu(2) is bonded in a 6-coordinate geometry to two equivalent Si(1), two equivalent Si(3), and two equivalent Si(5) atoms. In the third Eu site, Eu(3) is bonded in a 12-coordinate geometry to one Mg(2), one Mg(3), two equivalent Mg(4), two equivalent Mg(5), two equivalent Si(3), two equivalent Si(4), and two equivalent Si(5) atoms. There are five inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to one Mg(2), three equivalent Mg(1), two equivalent Eu(1), two equivalent Eu(2), and one Si(3) atom. In the second Si site, Si(2) is bonded in a 7-coordinate geometry to one Mg(2), one Mg(3), two equivalent Mg(4), two equivalent Mg(5), and one Eu(1) atom. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(5), two equivalent Eu(1), two equivalent Eu(2), two equivalent Eu(3), one Si(1), and one Si(5) atom. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(4), one Mg(5), two equivalent Mg(2), two equivalent Eu(1), and two equivalent Eu(3) atoms. In the fifth Si site, Si(5) is bonded in a 9-coordinate geometry to one Mg(4), three equivalent Mg(3), two equivalent Eu(2), two equivalent Eu(3), and one Si(3) atom.
Eu3(MgSi)5 crystallizes in the orthorhombic Pnma space group. There are five inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one Si(4) and three equivalent Si(1) atoms to form MgSi4 tetrahedra that share  a cornercorner with one Mg(4)Eu2Si4 tetrahedra,  a cornercorner with one Mg(5)Eu2Si4 tetrahedra,  a cornercorner with one Mg(2)EuSi4 tetrahedra, corners with two equivalent Mg(1)Si4 tetrahedra, edges with two equivalent Mg(2)EuSi4 tetrahedra, and edges with two equivalent Mg(1)Si4 tetrahedra. The Mg(1)-Si(4) bond length is 2.70 Å. There is one shorter (2.71 Å) and two longer (2.75 Å) Mg(1)-Si(1) bond lengths. In the second Mg site, Mg(2) is bonded to one Eu(3), one Si(1), one Si(2), and two equivalent Si(4) atoms to form distorted MgEuSi4 tetrahedra that share  a cornercorner with one Mg(1)Si4 tetrahedra, corners with two equivalent Mg(4)Eu2Si4 tetrahedra, corners with two equivalent Mg(2)EuSi4 tetrahedra, corners with two equivalent Mg(3)EuSi4 tetrahedra, edges with two equivalent Mg(4)Eu2Si4 tetrahedra, edges with two equivalent Mg(1)Si4 tetrahedra, and faces with two equivalent Mg(5)Eu2Si4 tetrahedra. The Mg(2)-Eu(3) bond length is 3.27 Å. The Mg(2)-Si(1) bond length is 2.71 Å. The Mg(2)-Si(2) bond length is 2.78 Å. Both Mg(2)-Si(4) bond lengths are 2.77 Å. In the third Mg site, Mg(3) is bonded to one Eu(3), one Si(2), and three equivalent Si(5) atoms to form distorted MgEuSi4 tetrahedra that share  a cornercorner with one Mg(4)Eu2Si4 tetrahedra, corners with two equivalent Mg(2)EuSi4 tetrahedra, corners with two equivalent Mg(3)EuSi4 tetrahedra, corners with four equivalent Mg(5)Eu2Si4 tetrahedra, edges with two equivalent Mg(3)EuSi4 tetrahedra, and faces with two equivalent Mg(4)Eu2Si4 tetrahedra. The Mg(3)-Eu(3) bond length is 3.27 Å. The Mg(3)-Si(2) bond length is 2.73 Å. There is one shorter (2.66 Å) and two longer (2.77 Å) Mg(3)-Si(5) bond lengths. In the fourth Mg site, Mg(4) is bonded to two equivalent Eu(3), one Si(4), one Si(5), and two equivalent Si(2) atoms to form distorted MgEu2Si4 tetrahedra that share  a cornercorner with one Mg(3)EuSi4 tetrahedra,  a cornercorner with one Mg(1)Si4 tetrahedra, corners with two equivalent Mg(2)EuSi4 tetrahedra, corners with four equivalent Mg(5)Eu2Si4 tetrahedra,  an edgeedge with one Mg(5)Eu2Si4 tetrahedra, edges with two equivalent Mg(4)Eu2Si4 tetrahedra, edges with two equivalent Mg(2)EuSi4 tetrahedra,  a faceface with one Mg(5)Eu2Si4 tetrahedra, and faces with two equivalent Mg(3)EuSi4 tetrahedra. Both Mg(4)-Eu(3) bond lengths are 3.31 Å. The Mg(4)-Si(4) bond length is 2.73 Å. The Mg(4)-Si(5) bond length is 2.74 Å. Both Mg(4)-Si(2) bond lengths are 2.78 Å. In the fifth Mg site, Mg(5) is bonded to two equivalent Eu(3), one Si(3), one Si(4), and two equivalent Si(2) atoms to form distorted MgEu2Si4 tetrahedra that share  a cornercorner with one Mg(1)Si4 tetrahedra, corners with four equivalent Mg(4)Eu2Si4 tetrahedra, corners with four equivalent Mg(3)EuSi4 tetrahedra,  an edgeedge with one Mg(4)Eu2Si4 tetrahedra, edges with two equivalent Mg(5)Eu2Si4 tetrahedra,  a faceface with one Mg(4)Eu2Si4 tetrahedra, and faces with two equivalent Mg(2)EuSi4 tetrahedra. Both Mg(5)-Eu(3) bond lengths are 3.24 Å. The Mg(5)-Si(3) bond length is 2.82 Å. The Mg(5)-Si(4) bond length is 2.74 Å. Both Mg(5)-Si(2) bond lengths are 2.73 Å. There are three inequivalent Eu sites. In the first Eu site, Eu(1) is bonded in a 7-coordinate geometry to one Si(2), two equivalent Si(1), two equivalent Si(3), and two equivalent Si(4) atoms. The Eu(1)-Si(2) bond length is 3.25 Å. Both Eu(1)-Si(1) bond lengths are 3.38 Å. Both Eu(1)-Si(3) bond lengths are 3.25 Å. Both Eu(1)-Si(4) bond lengths are 3.35 Å. In the second Eu site, Eu(2) is bonded in a 6-coordinate geometry to two equivalent Si(1), two equivalent Si(3), and two equivalent Si(5) atoms. Both Eu(2)-Si(1) bond lengths are 3.23 Å. Both Eu(2)-Si(3) bond lengths are 3.33 Å. Both Eu(2)-Si(5) bond lengths are 3.24 Å. In the third Eu site, Eu(3) is bonded in a 12-coordinate geometry to one Mg(2), one Mg(3), two equivalent Mg(4), two equivalent Mg(5), two equivalent Si(3), two equivalent Si(4), and two equivalent Si(5) atoms. Both Eu(3)-Si(3) bond lengths are 3.11 Å. Both Eu(3)-Si(4) bond lengths are 3.19 Å. Both Eu(3)-Si(5) bond lengths are 3.15 Å. There are five inequivalent Si sites. In the first Si site, Si(1) is bonded in a 9-coordinate geometry to one Mg(2), three equivalent Mg(1), two equivalent Eu(1), two equivalent Eu(2), and one Si(3) atom. The Si(1)-Si(3) bond length is 2.38 Å. In the second Si site, Si(2) is bonded in a 7-coordinate geometry to one Mg(2), one Mg(3), two equivalent Mg(4), two equivalent Mg(5), and one Eu(1) atom. In the third Si site, Si(3) is bonded in a 9-coordinate geometry to one Mg(5), two equivalent Eu(1), two equivalent Eu(2), two equivalent Eu(3), one Si(1), and one Si(5) atom. The Si(3)-Si(5) bond length is 2.41 Å. In the fourth Si site, Si(4) is bonded in a 9-coordinate geometry to one Mg(1), one Mg(4), one Mg(5), two equivalent Mg(2), two equivalent Eu(1), and two equivalent Eu(3) atoms. In the fifth Si site, Si(5) is bonded in a 9-coordinate geometry to one Mg(4), three equivalent Mg(3), two equivalent Eu(2), two equivalent Eu(3), and one Si(3) atom.