La2Si2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent La sites. In the first La site, La(1) is bonded in a 5-coordinate geometry to one O(1), one O(3), one O(4), and two equivalent O(7) atoms. In the second La site, La(2) is bonded in a 8-coordinate geometry to one Si(1), one O(1), one O(3), one O(6), two equivalent O(2), and two equivalent O(5) atoms. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a distorted trigonal non-coplanar geometry to one La(2), one O(1), one O(2), and one O(7) atom. In the second Si site, Si(2) is bonded in a tetrahedral geometry to one O(2), one O(3), one O(4), and one O(6) atom. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a trigonal non-coplanar geometry to one La(1), one La(2), and one Si(1) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to two equivalent La(2), one Si(1), and one Si(2) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to one La(1), one La(2), one Si(2), and one O(5) atom. In the fourth O site, O(4) is bonded in a distorted bent 150 degrees geometry to one La(1) and one Si(2) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent La(2) and one O(3) atom. In the sixth O site, O(6) is bonded in a bent 120 degrees geometry to one La(2) and one Si(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to two equivalent La(1) and one Si(1) atom.
La2Si2O7 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent La sites. In the first La site, La(1) is bonded in a 5-coordinate geometry to one O(1), one O(3), one O(4), and two equivalent O(7) atoms. The La(1)-O(1) bond length is 2.41 Å. The La(1)-O(3) bond length is 2.63 Å. The La(1)-O(4) bond length is 2.29 Å. There is one shorter (2.34 Å) and one longer (2.41 Å) La(1)-O(7) bond length. In the second La site, La(2) is bonded in a 8-coordinate geometry to one Si(1), one O(1), one O(3), one O(6), two equivalent O(2), and two equivalent O(5) atoms. The La(2)-Si(1) bond length is 3.17 Å. The La(2)-O(1) bond length is 2.37 Å. The La(2)-O(3) bond length is 2.69 Å. The La(2)-O(6) bond length is 2.29 Å. There is one shorter (2.56 Å) and one longer (3.09 Å) La(2)-O(2) bond length. There is one shorter (2.54 Å) and one longer (2.56 Å) La(2)-O(5) bond length. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a distorted trigonal non-coplanar geometry to one La(2), one O(1), one O(2), and one O(7) atom. The Si(1)-O(1) bond length is 1.70 Å. The Si(1)-O(2) bond length is 1.80 Å. The Si(1)-O(7) bond length is 1.66 Å. In the second Si site, Si(2) is bonded in a tetrahedral geometry to one O(2), one O(3), one O(4), and one O(6) atom. The Si(2)-O(2) bond length is 1.68 Å. The Si(2)-O(3) bond length is 1.77 Å. The Si(2)-O(4) bond length is 1.60 Å. The Si(2)-O(6) bond length is 1.61 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a trigonal non-coplanar geometry to one La(1), one La(2), and one Si(1) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to two equivalent La(2), one Si(1), and one Si(2) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to one La(1), one La(2), one Si(2), and one O(5) atom. The O(3)-O(5) bond length is 1.49 Å. In the fourth O site, O(4) is bonded in a distorted bent 150 degrees geometry to one La(1) and one Si(2) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent La(2) and one O(3) atom. In the sixth O site, O(6) is bonded in a bent 120 degrees geometry to one La(2) and one Si(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to two equivalent La(1) and one Si(1) atom.