Eu2Si2O7 crystallizes in the orthorhombic Pnma space group. Eu(1) is bonded to one O(1), one O(3), one O(5), two equivalent O(2), and two equivalent O(4) atoms to form distorted EuO7 pentagonal bipyramids that share corners with three equivalent Eu(1)O7 pentagonal bipyramids, corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, edges with two equivalent Eu(1)O7 pentagonal bipyramids,  an edgeedge with one Si(1)O4 tetrahedra, and  an edgeedge with one Si(2)O4 tetrahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form SiO4 tetrahedra that share corners with four equivalent Eu(1)O7 pentagonal bipyramids,  a cornercorner with one Si(2)O4 tetrahedra, and edges with two equivalent Eu(1)O7 pentagonal bipyramids. In the second Si site, Si(2) is bonded to one O(3), one O(5), and two equivalent O(4) atoms to form SiO4 tetrahedra that share corners with four equivalent Eu(1)O7 pentagonal bipyramids,  a cornercorner with one Si(1)O4 tetrahedra, and edges with two equivalent Eu(1)O7 pentagonal bipyramids. There are five inequivalent O sites. In the first O site, O(4) is bonded in a distorted trigonal planar geometry to two equivalent Eu(1) and one Si(2) atom. In the second O site, O(5) is bonded in a trigonal planar geometry to two equivalent Eu(1) and one Si(2) atom. In the third O site, O(1) is bonded in a trigonal planar geometry to two equivalent Eu(1) and one Si(1) atom. In the fourth O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Eu(1) and one Si(1) atom. In the fifth O site, O(3) is bonded in a distorted bent 150 degrees geometry to two equivalent Eu(1), one Si(1), and one Si(2) atom.
Eu2Si2O7 crystallizes in the orthorhombic Pnma space group. Eu(1) is bonded to one O(1), one O(3), one O(5), two equivalent O(2), and two equivalent O(4) atoms to form distorted EuO7 pentagonal bipyramids that share corners with three equivalent Eu(1)O7 pentagonal bipyramids, corners with two equivalent Si(1)O4 tetrahedra, corners with two equivalent Si(2)O4 tetrahedra, edges with two equivalent Eu(1)O7 pentagonal bipyramids,  an edgeedge with one Si(1)O4 tetrahedra, and  an edgeedge with one Si(2)O4 tetrahedra. The Eu(1)-O(1) bond length is 2.42 Å. The Eu(1)-O(3) bond length is 2.63 Å. The Eu(1)-O(5) bond length is 2.41 Å. There is one shorter (2.36 Å) and one longer (2.53 Å) Eu(1)-O(2) bond length. There is one shorter (2.31 Å) and one longer (2.48 Å) Eu(1)-O(4) bond length. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form SiO4 tetrahedra that share corners with four equivalent Eu(1)O7 pentagonal bipyramids,  a cornercorner with one Si(2)O4 tetrahedra, and edges with two equivalent Eu(1)O7 pentagonal bipyramids. The Si(1)-O(1) bond length is 1.63 Å. The Si(1)-O(3) bond length is 1.68 Å. Both Si(1)-O(2) bond lengths are 1.64 Å. In the second Si site, Si(2) is bonded to one O(3), one O(5), and two equivalent O(4) atoms to form SiO4 tetrahedra that share corners with four equivalent Eu(1)O7 pentagonal bipyramids,  a cornercorner with one Si(1)O4 tetrahedra, and edges with two equivalent Eu(1)O7 pentagonal bipyramids. The Si(2)-O(3) bond length is 1.68 Å. The Si(2)-O(5) bond length is 1.62 Å. Both Si(2)-O(4) bond lengths are 1.64 Å. There are five inequivalent O sites. In the first O site, O(4) is bonded in a distorted trigonal planar geometry to two equivalent Eu(1) and one Si(2) atom. In the second O site, O(5) is bonded in a trigonal planar geometry to two equivalent Eu(1) and one Si(2) atom. In the third O site, O(1) is bonded in a trigonal planar geometry to two equivalent Eu(1) and one Si(1) atom. In the fourth O site, O(2) is bonded in a 3-coordinate geometry to two equivalent Eu(1) and one Si(1) atom. In the fifth O site, O(3) is bonded in a distorted bent 150 degrees geometry to two equivalent Eu(1), one Si(1), and one Si(2) atom.