Pr2Ti2O7 crystallizes in the monoclinic P2_1 space group. There are four inequivalent Pr sites. In the first Pr site, Pr(1) is bonded in a 7-coordinate geometry to one O(1), one O(3), one O(5), two equivalent O(4), and two equivalent O(6) atoms. In the second Pr site, Pr(2) is bonded in a 8-coordinate geometry to one O(13), one O(14), one O(2), one O(4), one O(5), one O(6), and two equivalent O(3) atoms. In the third Pr site, Pr(3) is bonded in a 9-coordinate geometry to one O(1), one O(10), one O(7), one O(8), one O(9), two equivalent O(11), and two equivalent O(12) atoms. In the fourth Pr site, Pr(4) is bonded in a 8-coordinate geometry to one O(10), one O(11), one O(12), one O(13), one O(14), one O(2), one O(7), and one O(8) atom. There are four inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(1), one O(14), one O(2), one O(3), one O(5), and one O(7) atom to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 22-42°. In the second Ti site, Ti(2) is bonded to one O(1), one O(13), one O(2), one O(4), one O(6), and one O(8) atom to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 22-38°. In the third Ti site, Ti(3) is bonded to one O(10), one O(14), one O(7), one O(9), and two equivalent O(12) atoms to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 18-42°. In the fourth Ti site, Ti(4) is bonded to one O(10), one O(13), one O(8), one O(9), and two equivalent O(11) atoms to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 18-38°. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Pr(1), one Pr(3), one Ti(1), and one Ti(2) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Pr(2), one Pr(4), one Ti(1), and one Ti(2) atom. In the third O site, O(3) is bonded to one Pr(1), two equivalent Pr(2), and one Ti(1) atom to form distorted OPr3Ti tetrahedra that share  a cornercorner with one O(7)Pr2Ti2 tetrahedra, corners with two equivalent O(3)Pr3Ti tetrahedra, corners with two equivalent O(6)Pr3Ti tetrahedra, corners with four equivalent O(4)Pr3Ti tetrahedra, and  an edgeedge with one O(6)Pr3Ti tetrahedra. In the fourth O site, O(4) is bonded to one Pr(2), two equivalent Pr(1), and one Ti(2) atom to form distorted OPr3Ti tetrahedra that share  a cornercorner with one O(8)Pr2Ti2 tetrahedra, corners with two equivalent O(4)Pr3Ti tetrahedra, corners with four equivalent O(3)Pr3Ti tetrahedra, and edges with three equivalent O(6)Pr3Ti tetrahedra. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Pr(1), one Pr(2), and one Ti(1) atom. In the sixth O site, O(6) is bonded to one Pr(2), two equivalent Pr(1), and one Ti(2) atom to form distorted OPr3Ti tetrahedra that share  a cornercorner with one O(8)Pr2Ti2 tetrahedra, corners with two equivalent O(3)Pr3Ti tetrahedra, corners with two equivalent O(6)Pr3Ti tetrahedra,  an edgeedge with one O(3)Pr3Ti tetrahedra, and edges with three equivalent O(4)Pr3Ti tetrahedra. In the seventh O site, O(7) is bonded to one Pr(3), one Pr(4), one Ti(1), and one Ti(3) atom to form distorted OPr2Ti2 tetrahedra that share  a cornercorner with one O(10)Pr2Ti2 tetrahedra,  a cornercorner with one O(3)Pr3Ti tetrahedra, corners with two equivalent O(8)Pr2Ti2 tetrahedra, and  an edgeedge with one O(10)Pr2Ti2 tetrahedra. In the eighth O site, O(8) is bonded to one Pr(3), one Pr(4), one Ti(2), and one Ti(4) atom to form distorted OPr2Ti2 tetrahedra that share  a cornercorner with one O(10)Pr2Ti2 tetrahedra,  a cornercorner with one O(4)Pr3Ti tetrahedra,  a cornercorner with one O(6)Pr3Ti tetrahedra, corners with two equivalent O(7)Pr2Ti2 tetrahedra, and  an edgeedge with one O(10)Pr2Ti2 tetrahedra. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to one Pr(3), one Ti(3), and one Ti(4) atom. In the tenth O site, O(10) is bonded to one Pr(3), one Pr(4), one Ti(3), and one Ti(4) atom to form a mixture of distorted corner and edge-sharing OPr2Ti2 tetrahedra. In the eleventh O site, O(11) is bonded in a 5-coordinate geometry to one Pr(4), two equivalent Pr(3), and two equivalent Ti(4) atoms. In the twelfth O site, O(12) is bonded in a 5-coordinate geometry to one Pr(4), two equivalent Pr(3), and two equivalent Ti(3) atoms. In the thirteenth O site, O(13) is bonded in a 4-coordinate geometry to one Pr(2), one Pr(4), one Ti(2), and one Ti(4) atom. In the fourteenth O site, O(14) is bonded in a 4-coordinate geometry to one Pr(2), one Pr(4), one Ti(1), and one Ti(3) atom.
Pr2Ti2O7 crystallizes in the monoclinic P2_1 space group. There are four inequivalent Pr sites. In the first Pr site, Pr(1) is bonded in a 7-coordinate geometry to one O(1), one O(3), one O(5), two equivalent O(4), and two equivalent O(6) atoms. The Pr(1)-O(1) bond length is 2.48 Å. The Pr(1)-O(3) bond length is 2.44 Å. The Pr(1)-O(5) bond length is 2.34 Å. There is one shorter (2.43 Å) and one longer (2.45 Å) Pr(1)-O(4) bond length. There is one shorter (2.44 Å) and one longer (2.45 Å) Pr(1)-O(6) bond length. In the second Pr site, Pr(2) is bonded in a 8-coordinate geometry to one O(13), one O(14), one O(2), one O(4), one O(5), one O(6), and two equivalent O(3) atoms. The Pr(2)-O(13) bond length is 2.72 Å. The Pr(2)-O(14) bond length is 2.63 Å. The Pr(2)-O(2) bond length is 2.63 Å. The Pr(2)-O(4) bond length is 2.45 Å. The Pr(2)-O(5) bond length is 2.41 Å. The Pr(2)-O(6) bond length is 2.51 Å. There is one shorter (2.51 Å) and one longer (2.55 Å) Pr(2)-O(3) bond length. In the third Pr site, Pr(3) is bonded in a 9-coordinate geometry to one O(1), one O(10), one O(7), one O(8), one O(9), two equivalent O(11), and two equivalent O(12) atoms. The Pr(3)-O(1) bond length is 2.76 Å. The Pr(3)-O(10) bond length is 2.44 Å. The Pr(3)-O(7) bond length is 2.35 Å. The Pr(3)-O(8) bond length is 2.38 Å. The Pr(3)-O(9) bond length is 2.48 Å. There is one shorter (2.63 Å) and one longer (2.75 Å) Pr(3)-O(11) bond length. There is one shorter (2.63 Å) and one longer (2.72 Å) Pr(3)-O(12) bond length. In the fourth Pr site, Pr(4) is bonded in a 8-coordinate geometry to one O(10), one O(11), one O(12), one O(13), one O(14), one O(2), one O(7), and one O(8) atom. The Pr(4)-O(10) bond length is 2.39 Å. The Pr(4)-O(11) bond length is 2.46 Å. The Pr(4)-O(12) bond length is 2.44 Å. The Pr(4)-O(13) bond length is 2.59 Å. The Pr(4)-O(14) bond length is 2.62 Å. The Pr(4)-O(2) bond length is 2.49 Å. The Pr(4)-O(7) bond length is 2.48 Å. The Pr(4)-O(8) bond length is 2.53 Å. There are four inequivalent Ti sites. In the first Ti site, Ti(1) is bonded to one O(1), one O(14), one O(2), one O(3), one O(5), and one O(7) atom to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 22-42°. The Ti(1)-O(1) bond length is 1.99 Å. The Ti(1)-O(14) bond length is 2.29 Å. The Ti(1)-O(2) bond length is 1.99 Å. The Ti(1)-O(3) bond length is 1.90 Å. The Ti(1)-O(5) bond length is 1.77 Å. The Ti(1)-O(7) bond length is 2.04 Å. In the second Ti site, Ti(2) is bonded to one O(1), one O(13), one O(2), one O(4), one O(6), and one O(8) atom to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 22-38°. The Ti(2)-O(1) bond length is 1.96 Å. The Ti(2)-O(13) bond length is 2.23 Å. The Ti(2)-O(2) bond length is 2.01 Å. The Ti(2)-O(4) bond length is 1.86 Å. The Ti(2)-O(6) bond length is 1.85 Å. The Ti(2)-O(8) bond length is 1.98 Å. In the third Ti site, Ti(3) is bonded to one O(10), one O(14), one O(7), one O(9), and two equivalent O(12) atoms to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 18-42°. The Ti(3)-O(10) bond length is 2.00 Å. The Ti(3)-O(14) bond length is 1.83 Å. The Ti(3)-O(7) bond length is 1.92 Å. The Ti(3)-O(9) bond length is 1.98 Å. There is one shorter (1.96 Å) and one longer (2.27 Å) Ti(3)-O(12) bond length. In the fourth Ti site, Ti(4) is bonded to one O(10), one O(13), one O(8), one O(9), and two equivalent O(11) atoms to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedral tilt angles range from 18-38°. The Ti(4)-O(10) bond length is 2.00 Å. The Ti(4)-O(13) bond length is 1.83 Å. The Ti(4)-O(8) bond length is 1.93 Å. The Ti(4)-O(9) bond length is 1.97 Å. There is one shorter (1.95 Å) and one longer (2.23 Å) Ti(4)-O(11) bond length. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Pr(1), one Pr(3), one Ti(1), and one Ti(2) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Pr(2), one Pr(4), one Ti(1), and one Ti(2) atom. In the third O site, O(3) is bonded to one Pr(1), two equivalent Pr(2), and one Ti(1) atom to form distorted OPr3Ti tetrahedra that share  a cornercorner with one O(7)Pr2Ti2 tetrahedra, corners with two equivalent O(3)Pr3Ti tetrahedra, corners with two equivalent O(6)Pr3Ti tetrahedra, corners with four equivalent O(4)Pr3Ti tetrahedra, and  an edgeedge with one O(6)Pr3Ti tetrahedra. In the fourth O site, O(4) is bonded to one Pr(2), two equivalent Pr(1), and one Ti(2) atom to form distorted OPr3Ti tetrahedra that share  a cornercorner with one O(8)Pr2Ti2 tetrahedra, corners with two equivalent O(4)Pr3Ti tetrahedra, corners with four equivalent O(3)Pr3Ti tetrahedra, and edges with three equivalent O(6)Pr3Ti tetrahedra. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Pr(1), one Pr(2), and one Ti(1) atom. In the sixth O site, O(6) is bonded to one Pr(2), two equivalent Pr(1), and one Ti(2) atom to form distorted OPr3Ti tetrahedra that share  a cornercorner with one O(8)Pr2Ti2 tetrahedra, corners with two equivalent O(3)Pr3Ti tetrahedra, corners with two equivalent O(6)Pr3Ti tetrahedra,  an edgeedge with one O(3)Pr3Ti tetrahedra, and edges with three equivalent O(4)Pr3Ti tetrahedra. In the seventh O site, O(7) is bonded to one Pr(3), one Pr(4), one Ti(1), and one Ti(3) atom to form distorted OPr2Ti2 tetrahedra that share  a cornercorner with one O(10)Pr2Ti2 tetrahedra,  a cornercorner with one O(3)Pr3Ti tetrahedra, corners with two equivalent O(8)Pr2Ti2 tetrahedra, and  an edgeedge with one O(10)Pr2Ti2 tetrahedra. In the eighth O site, O(8) is bonded to one Pr(3), one Pr(4), one Ti(2), and one Ti(4) atom to form distorted OPr2Ti2 tetrahedra that share  a cornercorner with one O(10)Pr2Ti2 tetrahedra,  a cornercorner with one O(4)Pr3Ti tetrahedra,  a cornercorner with one O(6)Pr3Ti tetrahedra, corners with two equivalent O(7)Pr2Ti2 tetrahedra, and  an edgeedge with one O(10)Pr2Ti2 tetrahedra. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to one Pr(3), one Ti(3), and one Ti(4) atom. In the tenth O site, O(10) is bonded to one Pr(3), one Pr(4), one Ti(3), and one Ti(4) atom to form a mixture of distorted corner and edge-sharing OPr2Ti2 tetrahedra. In the eleventh O site, O(11) is bonded in a 5-coordinate geometry to one Pr(4), two equivalent Pr(3), and two equivalent Ti(4) atoms. In the twelfth O site, O(12) is bonded in a 5-coordinate geometry to one Pr(4), two equivalent Pr(3), and two equivalent Ti(3) atoms. In the thirteenth O site, O(13) is bonded in a 4-coordinate geometry to one Pr(2), one Pr(4), one Ti(2), and one Ti(4) atom. In the fourteenth O site, O(14) is bonded in a 4-coordinate geometry to one Pr(2), one Pr(4), one Ti(1), and one Ti(3) atom.