Eu5Si(O2Cl3)2 crystallizes in the monoclinic C2/c space group. There are three inequivalent Eu sites. In the first Eu site, Eu(1) is bonded in a 9-coordinate geometry to one O(1), one O(2), one Cl(2), one Cl(4), two equivalent Cl(1), and three equivalent Cl(3) atoms. In the second Eu site, Eu(2) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent Cl(1), two equivalent Cl(3), and two equivalent Cl(4) atoms. In the third Eu site, Eu(3) is bonded in a 7-coordinate geometry to one O(2), two equivalent O(1), one Cl(2), one Cl(4), two equivalent Cl(1), and two equivalent Cl(3) atoms. Si(1) is bonded in a tetrahedral geometry to two equivalent O(1) and two equivalent O(2) atoms. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Eu(1), two equivalent Eu(3), and one Si(1) atom. In the second O site, O(2) is bonded to one Eu(1), one Eu(2), one Eu(3), and one Si(1) atom to form distorted OEu3Si trigonal pyramids that share corners with four equivalent Cl(1)Eu5 trigonal bipyramids, edges with two equivalent Cl(4)Eu6 octahedra,  an edgeedge with one Cl(1)Eu5 trigonal bipyramid, and  an edgeedge with one O(2)Eu3Si trigonal pyramid. There are four inequivalent Cl sites. In the first Cl site, Cl(4) is bonded to two equivalent Eu(1), two equivalent Eu(2), and two equivalent Eu(3) atoms to form ClEu6 octahedra that share corners with two equivalent Cl(4)Eu6 octahedra, corners with six equivalent Cl(1)Eu5 trigonal bipyramids, edges with four equivalent O(2)Eu3Si trigonal pyramids, and faces with two equivalent Cl(1)Eu5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 25°. In the second Cl site, Cl(1) is bonded to one Eu(2), two equivalent Eu(1), and two equivalent Eu(3) atoms to form distorted ClEu5 trigonal bipyramids that share corners with three equivalent Cl(4)Eu6 octahedra,  a cornercorner with one Cl(1)Eu5 trigonal bipyramid, corners with four equivalent O(2)Eu3Si trigonal pyramids, edges with two equivalent Cl(1)Eu5 trigonal bipyramids,  an edgeedge with one O(2)Eu3Si trigonal pyramid, and  a faceface with one Cl(4)Eu6 octahedra. The corner-sharing octahedral tilt angles range from 37-66°. In the third Cl site, Cl(2) is bonded in a distorted see-saw-like geometry to two equivalent Eu(1) and two equivalent Eu(3) atoms. In the fourth Cl site, Cl(3) is bonded in a 6-coordinate geometry to one Eu(2), two equivalent Eu(3), and three equivalent Eu(1) atoms.
Eu5Si(O2Cl3)2 crystallizes in the monoclinic C2/c space group. There are three inequivalent Eu sites. In the first Eu site, Eu(1) is bonded in a 9-coordinate geometry to one O(1), one O(2), one Cl(2), one Cl(4), two equivalent Cl(1), and three equivalent Cl(3) atoms. The Eu(1)-O(1) bond length is 2.54 Å. The Eu(1)-O(2) bond length is 2.49 Å. The Eu(1)-Cl(2) bond length is 3.13 Å. The Eu(1)-Cl(4) bond length is 3.03 Å. There is one shorter (2.99 Å) and one longer (3.31 Å) Eu(1)-Cl(1) bond length. There are a spread of Eu(1)-Cl(3) bond distances ranging from 2.93-3.31 Å. In the second Eu site, Eu(2) is bonded in a 8-coordinate geometry to two equivalent O(2), two equivalent Cl(1), two equivalent Cl(3), and two equivalent Cl(4) atoms. Both Eu(2)-O(2) bond lengths are 2.48 Å. Both Eu(2)-Cl(1) bond lengths are 2.85 Å. Both Eu(2)-Cl(3) bond lengths are 2.94 Å. Both Eu(2)-Cl(4) bond lengths are 3.21 Å. In the third Eu site, Eu(3) is bonded in a 7-coordinate geometry to one O(2), two equivalent O(1), one Cl(2), one Cl(4), two equivalent Cl(1), and two equivalent Cl(3) atoms. The Eu(3)-O(2) bond length is 2.51 Å. There is one shorter (2.42 Å) and one longer (2.70 Å) Eu(3)-O(1) bond length. The Eu(3)-Cl(2) bond length is 3.05 Å. The Eu(3)-Cl(4) bond length is 3.24 Å. There is one shorter (2.92 Å) and one longer (3.21 Å) Eu(3)-Cl(1) bond length. There is one shorter (3.45 Å) and one longer (3.60 Å) Eu(3)-Cl(3) bond length. Si(1) is bonded in a tetrahedral geometry to two equivalent O(1) and two equivalent O(2) atoms. Both Si(1)-O(1) bond lengths are 1.63 Å. Both Si(1)-O(2) bond lengths are 1.64 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Eu(1), two equivalent Eu(3), and one Si(1) atom. In the second O site, O(2) is bonded to one Eu(1), one Eu(2), one Eu(3), and one Si(1) atom to form distorted OEu3Si trigonal pyramids that share corners with four equivalent Cl(1)Eu5 trigonal bipyramids, edges with two equivalent Cl(4)Eu6 octahedra,  an edgeedge with one Cl(1)Eu5 trigonal bipyramid, and  an edgeedge with one O(2)Eu3Si trigonal pyramid. There are four inequivalent Cl sites. In the first Cl site, Cl(4) is bonded to two equivalent Eu(1), two equivalent Eu(2), and two equivalent Eu(3) atoms to form ClEu6 octahedra that share corners with two equivalent Cl(4)Eu6 octahedra, corners with six equivalent Cl(1)Eu5 trigonal bipyramids, edges with four equivalent O(2)Eu3Si trigonal pyramids, and faces with two equivalent Cl(1)Eu5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 25°. In the second Cl site, Cl(1) is bonded to one Eu(2), two equivalent Eu(1), and two equivalent Eu(3) atoms to form distorted ClEu5 trigonal bipyramids that share corners with three equivalent Cl(4)Eu6 octahedra,  a cornercorner with one Cl(1)Eu5 trigonal bipyramid, corners with four equivalent O(2)Eu3Si trigonal pyramids, edges with two equivalent Cl(1)Eu5 trigonal bipyramids,  an edgeedge with one O(2)Eu3Si trigonal pyramid, and  a faceface with one Cl(4)Eu6 octahedra. The corner-sharing octahedral tilt angles range from 37-66°. In the third Cl site, Cl(2) is bonded in a distorted see-saw-like geometry to two equivalent Eu(1) and two equivalent Eu(3) atoms. In the fourth Cl site, Cl(3) is bonded in a 6-coordinate geometry to one Eu(2), two equivalent Eu(3), and three equivalent Eu(1) atoms.