PrNb3O9 crystallizes in the triclinic P-1 space group. There are two inequivalent Pr sites. In the first Pr site, Pr(1) is bonded in a 10-coordinate geometry to one O(12), one O(14), one O(17), one O(2), two equivalent O(1), two equivalent O(11), and two equivalent O(8) atoms. In the second Pr site, Pr(2) is bonded in a 12-coordinate geometry to one O(10), one O(13), one O(16), one O(3), one O(4), two equivalent O(15), two equivalent O(18), and three equivalent O(9) atoms. There are six inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(10), one O(12), one O(13), one O(2), one O(3), and one O(5) atom to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 12-26°. In the second Nb site, Nb(2) is bonded to one O(1), one O(11), one O(12), one O(2), one O(5), and one O(8) atom to form distorted corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 1-26°. In the third Nb site, Nb(3) is bonded to one O(1), one O(11), one O(14), one O(17), one O(6), and one O(8) atom to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 1-28°. In the fourth Nb site, Nb(4) is bonded to one O(13), one O(15), one O(18), one O(3), one O(6), and one O(9) atom to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 12-30°. In the fifth Nb site, Nb(5) is bonded to one O(15), one O(16), one O(18), one O(4), one O(7), and one O(9) atom to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 7-30°. In the sixth Nb site, Nb(6) is bonded to one O(10), one O(14), one O(16), one O(17), one O(4), and one O(7) atom to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 7-28°. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Pr(1), one Nb(2), and one Nb(3) atom to form a mixture of distorted corner and edge-sharing OPr2Nb2 trigonal pyramids. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Pr(1), one Nb(1), and one Nb(2) atom. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Pr(2), one Nb(1), and one Nb(4) atom. In the fourth O site, O(4) is bonded in a distorted T-shaped geometry to one Pr(2), one Nb(5), and one Nb(6) atom. In the fifth O site, O(5) is bonded in a linear geometry to one Nb(1) and one Nb(2) atom. In the sixth O site, O(6) is bonded in a linear geometry to one Nb(3) and one Nb(4) atom. In the seventh O site, O(7) is bonded in a linear geometry to one Nb(5) and one Nb(6) atom. In the eighth O site, O(8) is bonded to two equivalent Pr(1), one Nb(2), and one Nb(3) atom to form a mixture of distorted corner and edge-sharing OPr2Nb2 trigonal pyramids. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to three equivalent Pr(2), one Nb(4), and one Nb(5) atom. In the tenth O site, O(10) is bonded in a 3-coordinate geometry to one Pr(2), one Nb(1), and one Nb(6) atom. In the eleventh O site, O(11) is bonded in a linear geometry to two equivalent Pr(1), one Nb(2), and one Nb(3) atom. In the twelfth O site, O(12) is bonded in a distorted T-shaped geometry to one Pr(1), one Nb(1), and one Nb(2) atom. In the thirteenth O site, O(13) is bonded in a distorted linear geometry to one Pr(2), one Nb(1), and one Nb(4) atom. In the fourteenth O site, O(14) is bonded in a distorted T-shaped geometry to one Pr(1), one Nb(3), and one Nb(6) atom. In the fifteenth O site, O(15) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Pr(2), one Nb(4), and one Nb(5) atom. In the sixteenth O site, O(16) is bonded in a distorted linear geometry to one Pr(2), one Nb(5), and one Nb(6) atom. In the seventeenth O site, O(17) is bonded in a 3-coordinate geometry to one Pr(1), one Nb(3), and one Nb(6) atom. In the eighteenth O site, O(18) is bonded to two equivalent Pr(2), one Nb(4), and one Nb(5) atom to form distorted edge-sharing OPr2Nb2 tetrahedra.
PrNb3O9 crystallizes in the triclinic P-1 space group. There are two inequivalent Pr sites. In the first Pr site, Pr(1) is bonded in a 10-coordinate geometry to one O(12), one O(14), one O(17), one O(2), two equivalent O(1), two equivalent O(11), and two equivalent O(8) atoms. The Pr(1)-O(12) bond length is 2.67 Å. The Pr(1)-O(14) bond length is 2.66 Å. The Pr(1)-O(17) bond length is 2.58 Å. The Pr(1)-O(2) bond length is 2.58 Å. Both Pr(1)-O(1) bond lengths are 2.61 Å. Both Pr(1)-O(11) bond lengths are 2.82 Å. There is one shorter (2.43 Å) and one longer (2.44 Å) Pr(1)-O(8) bond length. In the second Pr site, Pr(2) is bonded in a 12-coordinate geometry to one O(10), one O(13), one O(16), one O(3), one O(4), two equivalent O(15), two equivalent O(18), and three equivalent O(9) atoms. The Pr(2)-O(10) bond length is 2.55 Å. The Pr(2)-O(13) bond length is 2.90 Å. The Pr(2)-O(16) bond length is 2.87 Å. The Pr(2)-O(3) bond length is 2.67 Å. The Pr(2)-O(4) bond length is 2.65 Å. There is one shorter (2.63 Å) and one longer (2.65 Å) Pr(2)-O(15) bond length. There is one shorter (2.52 Å) and one longer (2.54 Å) Pr(2)-O(18) bond length. There are a spread of Pr(2)-O(9) bond distances ranging from 2.51-3.11 Å. There are six inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(10), one O(12), one O(13), one O(2), one O(3), and one O(5) atom to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 12-26°. The Nb(1)-O(10) bond length is 1.99 Å. The Nb(1)-O(12) bond length is 1.99 Å. The Nb(1)-O(13) bond length is 2.02 Å. The Nb(1)-O(2) bond length is 1.99 Å. The Nb(1)-O(3) bond length is 2.02 Å. The Nb(1)-O(5) bond length is 2.01 Å. In the second Nb site, Nb(2) is bonded to one O(1), one O(11), one O(12), one O(2), one O(5), and one O(8) atom to form distorted corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 1-26°. The Nb(2)-O(1) bond length is 2.07 Å. The Nb(2)-O(11) bond length is 2.02 Å. The Nb(2)-O(12) bond length is 1.97 Å. The Nb(2)-O(2) bond length is 2.00 Å. The Nb(2)-O(5) bond length is 1.89 Å. The Nb(2)-O(8) bond length is 2.19 Å. In the third Nb site, Nb(3) is bonded to one O(1), one O(11), one O(14), one O(17), one O(6), and one O(8) atom to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 1-28°. The Nb(3)-O(1) bond length is 2.08 Å. The Nb(3)-O(11) bond length is 2.02 Å. The Nb(3)-O(14) bond length is 1.97 Å. The Nb(3)-O(17) bond length is 2.00 Å. The Nb(3)-O(6) bond length is 1.90 Å. The Nb(3)-O(8) bond length is 2.16 Å. In the fourth Nb site, Nb(4) is bonded to one O(13), one O(15), one O(18), one O(3), one O(6), and one O(9) atom to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 12-30°. The Nb(4)-O(13) bond length is 1.92 Å. The Nb(4)-O(15) bond length is 2.08 Å. The Nb(4)-O(18) bond length is 2.12 Å. The Nb(4)-O(3) bond length is 1.94 Å. The Nb(4)-O(6) bond length is 1.99 Å. The Nb(4)-O(9) bond length is 2.04 Å. In the fifth Nb site, Nb(5) is bonded to one O(15), one O(16), one O(18), one O(4), one O(7), and one O(9) atom to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 7-30°. The Nb(5)-O(15) bond length is 2.04 Å. The Nb(5)-O(16) bond length is 1.93 Å. The Nb(5)-O(18) bond length is 2.09 Å. The Nb(5)-O(4) bond length is 1.97 Å. The Nb(5)-O(7) bond length is 1.94 Å. The Nb(5)-O(9) bond length is 2.13 Å. In the sixth Nb site, Nb(6) is bonded to one O(10), one O(14), one O(16), one O(17), one O(4), and one O(7) atom to form corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles range from 7-28°. The Nb(6)-O(10) bond length is 2.09 Å. The Nb(6)-O(14) bond length is 2.00 Å. The Nb(6)-O(16) bond length is 2.02 Å. The Nb(6)-O(17) bond length is 2.00 Å. The Nb(6)-O(4) bond length is 2.01 Å. The Nb(6)-O(7) bond length is 1.94 Å. There are eighteen inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Pr(1), one Nb(2), and one Nb(3) atom to form a mixture of distorted corner and edge-sharing OPr2Nb2 trigonal pyramids. In the second O site, O(2) is bonded in a distorted T-shaped geometry to one Pr(1), one Nb(1), and one Nb(2) atom. In the third O site, O(3) is bonded in a distorted T-shaped geometry to one Pr(2), one Nb(1), and one Nb(4) atom. In the fourth O site, O(4) is bonded in a distorted T-shaped geometry to one Pr(2), one Nb(5), and one Nb(6) atom. In the fifth O site, O(5) is bonded in a linear geometry to one Nb(1) and one Nb(2) atom. In the sixth O site, O(6) is bonded in a linear geometry to one Nb(3) and one Nb(4) atom. In the seventh O site, O(7) is bonded in a linear geometry to one Nb(5) and one Nb(6) atom. In the eighth O site, O(8) is bonded to two equivalent Pr(1), one Nb(2), and one Nb(3) atom to form a mixture of distorted corner and edge-sharing OPr2Nb2 trigonal pyramids. In the ninth O site, O(9) is bonded in a 3-coordinate geometry to three equivalent Pr(2), one Nb(4), and one Nb(5) atom. In the tenth O site, O(10) is bonded in a 3-coordinate geometry to one Pr(2), one Nb(1), and one Nb(6) atom. In the eleventh O site, O(11) is bonded in a linear geometry to two equivalent Pr(1), one Nb(2), and one Nb(3) atom. In the twelfth O site, O(12) is bonded in a distorted T-shaped geometry to one Pr(1), one Nb(1), and one Nb(2) atom. In the thirteenth O site, O(13) is bonded in a distorted linear geometry to one Pr(2), one Nb(1), and one Nb(4) atom. In the fourteenth O site, O(14) is bonded in a distorted T-shaped geometry to one Pr(1), one Nb(3), and one Nb(6) atom. In the fifteenth O site, O(15) is bonded in a distorted rectangular see-saw-like geometry to two equivalent Pr(2), one Nb(4), and one Nb(5) atom. In the sixteenth O site, O(16) is bonded in a distorted linear geometry to one Pr(2), one Nb(5), and one Nb(6) atom. In the seventeenth O site, O(17) is bonded in a 3-coordinate geometry to one Pr(1), one Nb(3), and one Nb(6) atom. In the eighteenth O site, O(18) is bonded to two equivalent Pr(2), one Nb(4), and one Nb(5) atom to form distorted edge-sharing OPr2Nb2 tetrahedra.