Y2Si2O7 crystallizes in the triclinic P-1 space group. There are four inequivalent Y sites. In the first Y site, Y(1) is bonded in a 8-coordinate geometry to one O(10), one O(11), one O(13), one O(14), one O(5), one O(7), and two equivalent O(4) atoms. In the second Y site, Y(2) is bonded in a 8-coordinate geometry to one O(12), one O(14), one O(2), one O(5), one O(6), one O(7), one O(8), and one O(9) atom. In the third Y site, Y(3) is bonded to one O(11), one O(13), one O(14), one O(3), one O(4), and one O(6) atom to form distorted YO6 octahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra, and corners with three equivalent Si(4)O4 tetrahedra. In the fourth Y site, Y(4) is bonded in a 7-coordinate geometry to one O(10), one O(12), one O(2), one O(7), one O(9), and two equivalent O(8) atoms. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(12), one O(3), one O(5), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Y(3)O6 octahedra and  a cornercorner with one Si(4)O4 tetrahedra. The corner-sharing octahedral tilt angles are 55°. In the second Si site, Si(2) is bonded to one O(2), one O(6), one O(7), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Y(3)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. In the third Si site, Si(3) is bonded to one O(1), one O(10), one O(14), and one O(4) atom to form SiO4 tetrahedra that share corners with two equivalent Y(3)O6 octahedra and  a cornercorner with one Si(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 48-67°. In the fourth Si site, Si(4) is bonded to one O(1), one O(11), one O(13), and one O(3) atom to form SiO4 tetrahedra that share corners with three equivalent Y(3)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 64-66°. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one Si(3) and one Si(4) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Y(2), one Y(4), and one Si(2) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Y(3), one Si(1), and one Si(4) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Y(3), two equivalent Y(1), and one Si(3) atom. In the fifth O site, O(5) is bonded in a 1-coordinate geometry to one Y(1), one Y(2), and one Si(1) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Y(2), one Y(3), and one Si(2) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Y(1), one Y(2), one Y(4), and one Si(2) atom. In the eighth O site, O(8) is bonded to one Y(2), two equivalent Y(4), and one Si(2) atom to form distorted edge-sharing OY3Si tetrahedra. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to one Y(2), one Y(4), and one Si(1) atom. In the tenth O site, O(10) is bonded in a 3-coordinate geometry to one Y(1), one Y(4), and one Si(3) atom. In the eleventh O site, O(11) is bonded in a distorted trigonal planar geometry to one Y(1), one Y(3), and one Si(4) atom. In the twelfth O site, O(12) is bonded in a 3-coordinate geometry to one Y(2), one Y(4), and one Si(1) atom. In the thirteenth O site, O(13) is bonded in a distorted trigonal planar geometry to one Y(1), one Y(3), and one Si(4) atom. In the fourteenth O site, O(14) is bonded in a 4-coordinate geometry to one Y(1), one Y(2), one Y(3), and one Si(3) atom.
Y2Si2O7 crystallizes in the triclinic P-1 space group. There are four inequivalent Y sites. In the first Y site, Y(1) is bonded in a 8-coordinate geometry to one O(10), one O(11), one O(13), one O(14), one O(5), one O(7), and two equivalent O(4) atoms. The Y(1)-O(10) bond length is 2.32 Å. The Y(1)-O(11) bond length is 2.31 Å. The Y(1)-O(13) bond length is 2.27 Å. The Y(1)-O(14) bond length is 2.43 Å. The Y(1)-O(5) bond length is 2.58 Å. The Y(1)-O(7) bond length is 2.24 Å. There is one shorter (2.54 Å) and one longer (2.84 Å) Y(1)-O(4) bond length. In the second Y site, Y(2) is bonded in a 8-coordinate geometry to one O(12), one O(14), one O(2), one O(5), one O(6), one O(7), one O(8), and one O(9) atom. The Y(2)-O(12) bond length is 2.31 Å. The Y(2)-O(14) bond length is 2.56 Å. The Y(2)-O(2) bond length is 2.32 Å. The Y(2)-O(5) bond length is 2.36 Å. The Y(2)-O(6) bond length is 2.38 Å. The Y(2)-O(7) bond length is 2.73 Å. The Y(2)-O(8) bond length is 2.41 Å. The Y(2)-O(9) bond length is 2.55 Å. In the third Y site, Y(3) is bonded to one O(11), one O(13), one O(14), one O(3), one O(4), and one O(6) atom to form distorted YO6 octahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, corners with two equivalent Si(3)O4 tetrahedra, and corners with three equivalent Si(4)O4 tetrahedra. The Y(3)-O(11) bond length is 2.27 Å. The Y(3)-O(13) bond length is 2.30 Å. The Y(3)-O(14) bond length is 2.36 Å. The Y(3)-O(3) bond length is 2.41 Å. The Y(3)-O(4) bond length is 2.31 Å. The Y(3)-O(6) bond length is 2.21 Å. In the fourth Y site, Y(4) is bonded in a 7-coordinate geometry to one O(10), one O(12), one O(2), one O(7), one O(9), and two equivalent O(8) atoms. The Y(4)-O(10) bond length is 2.42 Å. The Y(4)-O(12) bond length is 2.27 Å. The Y(4)-O(2) bond length is 2.42 Å. The Y(4)-O(7) bond length is 2.34 Å. The Y(4)-O(9) bond length is 2.35 Å. There is one shorter (2.38 Å) and one longer (2.41 Å) Y(4)-O(8) bond length. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(12), one O(3), one O(5), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Y(3)O6 octahedra and  a cornercorner with one Si(4)O4 tetrahedra. The corner-sharing octahedral tilt angles are 55°. The Si(1)-O(12) bond length is 1.63 Å. The Si(1)-O(3) bond length is 1.75 Å. The Si(1)-O(5) bond length is 1.65 Å. The Si(1)-O(9) bond length is 1.63 Å. In the second Si site, Si(2) is bonded to one O(2), one O(6), one O(7), and one O(8) atom to form SiO4 tetrahedra that share  a cornercorner with one Y(3)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. The Si(2)-O(2) bond length is 1.63 Å. The Si(2)-O(6) bond length is 1.62 Å. The Si(2)-O(7) bond length is 1.64 Å. The Si(2)-O(8) bond length is 1.67 Å. In the third Si site, Si(3) is bonded to one O(1), one O(10), one O(14), and one O(4) atom to form SiO4 tetrahedra that share corners with two equivalent Y(3)O6 octahedra and  a cornercorner with one Si(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 48-67°. The Si(3)-O(1) bond length is 1.68 Å. The Si(3)-O(10) bond length is 1.63 Å. The Si(3)-O(14) bond length is 1.66 Å. The Si(3)-O(4) bond length is 1.65 Å. In the fourth Si site, Si(4) is bonded to one O(1), one O(11), one O(13), and one O(3) atom to form SiO4 tetrahedra that share corners with three equivalent Y(3)O6 octahedra,  a cornercorner with one Si(1)O4 tetrahedra, and  a cornercorner with one Si(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 64-66°. The Si(4)-O(1) bond length is 1.66 Å. The Si(4)-O(11) bond length is 1.61 Å. The Si(4)-O(13) bond length is 1.64 Å. The Si(4)-O(3) bond length is 1.67 Å. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a bent 120 degrees geometry to one Si(3) and one Si(4) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Y(2), one Y(4), and one Si(2) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Y(3), one Si(1), and one Si(4) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Y(3), two equivalent Y(1), and one Si(3) atom. In the fifth O site, O(5) is bonded in a 1-coordinate geometry to one Y(1), one Y(2), and one Si(1) atom. In the sixth O site, O(6) is bonded in a distorted trigonal planar geometry to one Y(2), one Y(3), and one Si(2) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Y(1), one Y(2), one Y(4), and one Si(2) atom. In the eighth O site, O(8) is bonded to one Y(2), two equivalent Y(4), and one Si(2) atom to form distorted edge-sharing OY3Si tetrahedra. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to one Y(2), one Y(4), and one Si(1) atom. In the tenth O site, O(10) is bonded in a 3-coordinate geometry to one Y(1), one Y(4), and one Si(3) atom. In the eleventh O site, O(11) is bonded in a distorted trigonal planar geometry to one Y(1), one Y(3), and one Si(4) atom. In the twelfth O site, O(12) is bonded in a 3-coordinate geometry to one Y(2), one Y(4), and one Si(1) atom. In the thirteenth O site, O(13) is bonded in a distorted trigonal planar geometry to one Y(1), one Y(3), and one Si(4) atom. In the fourteenth O site, O(14) is bonded in a 4-coordinate geometry to one Y(1), one Y(2), one Y(3), and one Si(3) atom.