Tb2Si2O7 crystallizes in the triclinic P-1 space group. There are four inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 8-coordinate geometry to one O(1), one O(10), one O(11), one O(2), one O(3), one O(4), one O(7), and one O(9) atom. In the second Tb site, Tb(2) is bonded in a 6-coordinate geometry to one O(12), one O(13), one O(14), one O(3), one O(6), and one O(7) atom. In the third Tb site, Tb(3) is bonded in a 8-coordinate geometry to one O(1), one O(10), one O(13), one O(14), one O(5), one O(7), and two equivalent O(6) atoms. In the fourth Tb site, Tb(4) is bonded in a 7-coordinate geometry to one O(1), one O(11), one O(4), one O(5), one O(9), and two equivalent O(2) atoms. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(5), one O(6), one O(7), and one O(8) atom to form corner-sharing SiO4 tetrahedra. In the second Si site, Si(2) is bonded to one O(12), one O(13), one O(14), and one O(8) atom to form corner-sharing SiO4 tetrahedra. In the third Si site, Si(3) is bonded to one O(10), one O(11), one O(12), and one O(9) atom to form corner-sharing SiO4 tetrahedra. In the fourth Si site, Si(4) is bonded in a tetrahedral geometry to one O(1), one O(2), one O(3), and one O(4) atom. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Tb(1), one Tb(3), one Tb(4), and one Si(4) atom. In the second O site, O(2) is bonded to one Tb(1), two equivalent Tb(4), and one Si(4) atom to form distorted edge-sharing OTb3Si tetrahedra. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Tb(1), one Tb(2), and one Si(4) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Tb(1), one Tb(4), and one Si(4) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Tb(3), one Tb(4), and one Si(1) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Tb(2), two equivalent Tb(3), and one Si(1) atom. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Tb(1), one Tb(2), one Tb(3), and one Si(1) atom. In the eighth O site, O(8) is bonded in a bent 120 degrees geometry to one Si(1) and one Si(2) atom. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to one Tb(1), one Tb(4), and one Si(3) atom. In the tenth O site, O(10) is bonded in a 1-coordinate geometry to one Tb(1), one Tb(3), and one Si(3) atom. In the eleventh O site, O(11) is bonded in a 3-coordinate geometry to one Tb(1), one Tb(4), and one Si(3) atom. In the twelfth O site, O(12) is bonded in a distorted trigonal planar geometry to one Tb(2), one Si(2), and one Si(3) atom. In the thirteenth O site, O(13) is bonded in a 3-coordinate geometry to one Tb(2), one Tb(3), and one Si(2) atom. In the fourteenth O site, O(14) is bonded in a distorted trigonal planar geometry to one Tb(2), one Tb(3), and one Si(2) atom.
Tb2Si2O7 crystallizes in the triclinic P-1 space group. There are four inequivalent Tb sites. In the first Tb site, Tb(1) is bonded in a 8-coordinate geometry to one O(1), one O(10), one O(11), one O(2), one O(3), one O(4), one O(7), and one O(9) atom. The Tb(1)-O(1) bond length is 2.69 Å. The Tb(1)-O(10) bond length is 2.35 Å. The Tb(1)-O(11) bond length is 2.50 Å. The Tb(1)-O(2) bond length is 2.40 Å. The Tb(1)-O(3) bond length is 2.36 Å. The Tb(1)-O(4) bond length is 2.31 Å. The Tb(1)-O(7) bond length is 2.53 Å. The Tb(1)-O(9) bond length is 2.29 Å. In the second Tb site, Tb(2) is bonded in a 6-coordinate geometry to one O(12), one O(13), one O(14), one O(3), one O(6), and one O(7) atom. The Tb(2)-O(12) bond length is 2.40 Å. The Tb(2)-O(13) bond length is 2.27 Å. The Tb(2)-O(14) bond length is 2.27 Å. The Tb(2)-O(3) bond length is 2.20 Å. The Tb(2)-O(6) bond length is 2.30 Å. The Tb(2)-O(7) bond length is 2.35 Å. In the third Tb site, Tb(3) is bonded in a 8-coordinate geometry to one O(1), one O(10), one O(13), one O(14), one O(5), one O(7), and two equivalent O(6) atoms. The Tb(3)-O(1) bond length is 2.24 Å. The Tb(3)-O(10) bond length is 2.54 Å. The Tb(3)-O(13) bond length is 2.26 Å. The Tb(3)-O(14) bond length is 2.30 Å. The Tb(3)-O(5) bond length is 2.31 Å. The Tb(3)-O(7) bond length is 2.41 Å. There is one shorter (2.52 Å) and one longer (2.77 Å) Tb(3)-O(6) bond length. In the fourth Tb site, Tb(4) is bonded in a 7-coordinate geometry to one O(1), one O(11), one O(4), one O(5), one O(9), and two equivalent O(2) atoms. The Tb(4)-O(1) bond length is 2.33 Å. The Tb(4)-O(11) bond length is 2.34 Å. The Tb(4)-O(4) bond length is 2.38 Å. The Tb(4)-O(5) bond length is 2.41 Å. The Tb(4)-O(9) bond length is 2.26 Å. There is one shorter (2.36 Å) and one longer (2.40 Å) Tb(4)-O(2) bond length. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(5), one O(6), one O(7), and one O(8) atom to form corner-sharing SiO4 tetrahedra. The Si(1)-O(5) bond length is 1.61 Å. The Si(1)-O(6) bond length is 1.63 Å. The Si(1)-O(7) bond length is 1.65 Å. The Si(1)-O(8) bond length is 1.67 Å. In the second Si site, Si(2) is bonded to one O(12), one O(13), one O(14), and one O(8) atom to form corner-sharing SiO4 tetrahedra. The Si(2)-O(12) bond length is 1.65 Å. The Si(2)-O(13) bond length is 1.62 Å. The Si(2)-O(14) bond length is 1.59 Å. The Si(2)-O(8) bond length is 1.65 Å. In the third Si site, Si(3) is bonded to one O(10), one O(11), one O(12), and one O(9) atom to form corner-sharing SiO4 tetrahedra. The Si(3)-O(10) bond length is 1.63 Å. The Si(3)-O(11) bond length is 1.61 Å. The Si(3)-O(12) bond length is 1.72 Å. The Si(3)-O(9) bond length is 1.61 Å. In the fourth Si site, Si(4) is bonded in a tetrahedral geometry to one O(1), one O(2), one O(3), and one O(4) atom. The Si(4)-O(1) bond length is 1.63 Å. The Si(4)-O(2) bond length is 1.65 Å. The Si(4)-O(3) bond length is 1.61 Å. The Si(4)-O(4) bond length is 1.61 Å. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Tb(1), one Tb(3), one Tb(4), and one Si(4) atom. In the second O site, O(2) is bonded to one Tb(1), two equivalent Tb(4), and one Si(4) atom to form distorted edge-sharing OTb3Si tetrahedra. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Tb(1), one Tb(2), and one Si(4) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Tb(1), one Tb(4), and one Si(4) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Tb(3), one Tb(4), and one Si(1) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Tb(2), two equivalent Tb(3), and one Si(1) atom. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Tb(1), one Tb(2), one Tb(3), and one Si(1) atom. In the eighth O site, O(8) is bonded in a bent 120 degrees geometry to one Si(1) and one Si(2) atom. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to one Tb(1), one Tb(4), and one Si(3) atom. In the tenth O site, O(10) is bonded in a 1-coordinate geometry to one Tb(1), one Tb(3), and one Si(3) atom. In the eleventh O site, O(11) is bonded in a 3-coordinate geometry to one Tb(1), one Tb(4), and one Si(3) atom. In the twelfth O site, O(12) is bonded in a distorted trigonal planar geometry to one Tb(2), one Si(2), and one Si(3) atom. In the thirteenth O site, O(13) is bonded in a 3-coordinate geometry to one Tb(2), one Tb(3), and one Si(2) atom. In the fourteenth O site, O(14) is bonded in a distorted trigonal planar geometry to one Tb(2), one Tb(3), and one Si(2) atom.