FeP2O7 crystallizes in the triclinic P1 space group. There are four inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(1), one O(14), one O(17), one O(24), one O(27), and one O(7) atom to form FeO6 octahedra that share  a cornercorner with one P(1)O4 tetrahedra,  a cornercorner with one P(2)O4 tetrahedra,  a cornercorner with one P(4)O4 tetrahedra,  a cornercorner with one P(5)O4 tetrahedra, corners with two equivalent P(3)O4 tetrahedra, and  a cornercorner with one Fe(4)O6 trigonal bipyramid. In the second Fe site, Fe(2) is bonded to one O(10), one O(12), one O(20), one O(23), one O(4), and one O(8) atom to form FeO6 octahedra that share  a cornercorner with one P(1)O4 tetrahedra,  a cornercorner with one P(4)O4 tetrahedra,  a cornercorner with one P(6)O4 tetrahedra,  a cornercorner with one P(8)O4 tetrahedra, corners with two equivalent P(7)O4 tetrahedra, and  a cornercorner with one Fe(3)O6 trigonal bipyramid. In the third Fe site, Fe(3) is bonded to one O(10), one O(13), one O(21), one O(25), one O(5), and one O(6) atom to form distorted FeO6 trigonal bipyramids that share  a cornercorner with one Fe(2)O6 octahedra,  a cornercorner with one P(5)O4 tetrahedra,  a cornercorner with one P(6)O4 tetrahedra,  a cornercorner with one P(7)O4 tetrahedra,  a cornercorner with one P(8)O4 tetrahedra, and  an edgeedge with one P(4)O4 tetrahedra. The corner-sharing octahedral tilt angles are 57°. In the fourth Fe site, Fe(4) is bonded to one O(1), one O(11), one O(15), one O(2), one O(22), and one O(9) atom to form distorted FeO6 trigonal bipyramids that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one P(2)O4 tetrahedra,  a cornercorner with one P(3)O4 tetrahedra,  a cornercorner with one P(5)O4 tetrahedra,  a cornercorner with one P(8)O4 tetrahedra, and  an edgeedge with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 57°. There are eight inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(19), one O(22), and one O(8) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one Fe(2)O6 octahedra,  a cornercorner with one P(7)O4 tetrahedra, and  an edgeedge with one Fe(4)O6 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 43-46°. In the second P site, P(2) is bonded to one O(16), one O(27), one O(28), and one O(9) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one P(8)O4 tetrahedra, and  a cornercorner with one Fe(4)O6 trigonal bipyramid. The corner-sharing octahedral tilt angles are 41°. In the third P site, P(3) is bonded to one O(14), one O(15), one O(24), and one O(3) atom to form PO4 tetrahedra that share corners with two equivalent Fe(1)O6 octahedra,  a cornercorner with one P(4)O4 tetrahedra, and  a cornercorner with one Fe(4)O6 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 31-49°. In the fourth P site, P(4) is bonded to one O(10), one O(17), one O(25), and one O(3) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one Fe(2)O6 octahedra,  a cornercorner with one P(3)O4 tetrahedra, and  an edgeedge with one Fe(3)O6 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 43-46°. In the fifth P site, P(5) is bonded to one O(11), one O(18), one O(5), and one O(7) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one P(6)O4 tetrahedra,  a cornercorner with one Fe(3)O6 trigonal bipyramid, and  a cornercorner with one Fe(4)O6 trigonal bipyramid. The corner-sharing octahedral tilt angles are 38°. In the sixth P site, P(6) is bonded to one O(18), one O(20), one O(21), and one O(26) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra,  a cornercorner with one P(5)O4 tetrahedra, and  a cornercorner with one Fe(3)O6 trigonal bipyramid. The corner-sharing octahedral tilt angles are 41°. In the seventh P site, P(7) is bonded to one O(19), one O(23), one O(4), and one O(6) atom to form PO4 tetrahedra that share corners with two equivalent Fe(2)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra, and  a cornercorner with one Fe(3)O6 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 31-49°. In the eighth P site, P(8) is bonded to one O(12), one O(13), one O(16), and one O(2) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra,  a cornercorner with one P(2)O4 tetrahedra,  a cornercorner with one Fe(3)O6 trigonal bipyramid, and  a cornercorner with one Fe(4)O6 trigonal bipyramid. The corner-sharing octahedral tilt angles are 38°. There are twenty-eight inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to one Fe(1), one Fe(4), and one P(1) atom. In the second O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Fe(4) and one P(8) atom. In the third O site, O(3) is bonded in a bent 120 degrees geometry to one P(3) and one P(4) atom. In the fourth O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Fe(2) and one P(7) atom. In the fifth O site, O(5) is bonded in a distorted bent 150 degrees geometry to one Fe(3) and one P(5) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Fe(3) and one P(7) atom. In the seventh O site, O(7) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(5) atom. In the eighth O site, O(8) is bonded in a distorted bent 120 degrees geometry to one Fe(2) and one P(1) atom. In the ninth O site, O(9) is bonded in a bent 150 degrees geometry to one Fe(4) and one P(2) atom. In the tenth O site, O(10) is bonded in a 2-coordinate geometry to one Fe(2), one Fe(3), and one P(4) atom. In the eleventh O site, O(11) is bonded in a bent 150 degrees geometry to one Fe(4) and one P(5) atom. In the twelfth O site, O(12) is bonded in a bent 150 degrees geometry to one Fe(2) and one P(8) atom. In the thirteenth O site, O(13) is bonded in a bent 150 degrees geometry to one Fe(3) and one P(8) atom. In the fourteenth O site, O(14) is bonded in a distorted bent 120 degrees geometry to one Fe(1) and one P(3) atom. In the fifteenth O site, O(15) is bonded in a bent 150 degrees geometry to one Fe(4) and one P(3) atom. In the sixteenth O site, O(16) is bonded in a distorted bent 120 degrees geometry to one P(2) and one P(8) atom. In the seventeenth O site, O(17) is bonded in a distorted bent 120 degrees geometry to one Fe(1) and one P(4) atom. In the eighteenth O site, O(18) is bonded in a distorted bent 120 degrees geometry to one P(5) and one P(6) atom. In the nineteenth O site, O(19) is bonded in a bent 120 degrees geometry to one P(1) and one P(7) atom. In the twentieth O site, O(20) is bonded in a bent 150 degrees geometry to one Fe(2) and one P(6) atom. In the twenty-first O site, O(21) is bonded in a bent 150 degrees geometry to one Fe(3) and one P(6) atom. In the twenty-second O site, O(22) is bonded in a water-like geometry to one Fe(4) and one P(1) atom. In the twenty-third O site, O(23) is bonded in a bent 150 degrees geometry to one Fe(2) and one P(7) atom. In the twenty-fourth O site, O(24) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(3) atom. In the twenty-fifth O site, O(25) is bonded in a water-like geometry to one Fe(3) and one P(4) atom. In the twenty-sixth O site, O(26) is bonded in a single-bond geometry to one P(6) atom. In the twenty-seventh O site, O(27) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(2) atom. In the twenty-eighth O site, O(28) is bonded in a single-bond geometry to one P(2) atom.
FeP2O7 crystallizes in the triclinic P1 space group. There are four inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(1), one O(14), one O(17), one O(24), one O(27), and one O(7) atom to form FeO6 octahedra that share  a cornercorner with one P(1)O4 tetrahedra,  a cornercorner with one P(2)O4 tetrahedra,  a cornercorner with one P(4)O4 tetrahedra,  a cornercorner with one P(5)O4 tetrahedra, corners with two equivalent P(3)O4 tetrahedra, and  a cornercorner with one Fe(4)O6 trigonal bipyramid. The Fe(1)-O(1) bond length is 2.07 Å. The Fe(1)-O(14) bond length is 2.02 Å. The Fe(1)-O(17) bond length is 1.97 Å. The Fe(1)-O(24) bond length is 2.05 Å. The Fe(1)-O(27) bond length is 1.96 Å. The Fe(1)-O(7) bond length is 1.99 Å. In the second Fe site, Fe(2) is bonded to one O(10), one O(12), one O(20), one O(23), one O(4), and one O(8) atom to form FeO6 octahedra that share  a cornercorner with one P(1)O4 tetrahedra,  a cornercorner with one P(4)O4 tetrahedra,  a cornercorner with one P(6)O4 tetrahedra,  a cornercorner with one P(8)O4 tetrahedra, corners with two equivalent P(7)O4 tetrahedra, and  a cornercorner with one Fe(3)O6 trigonal bipyramid. The Fe(2)-O(10) bond length is 2.07 Å. The Fe(2)-O(12) bond length is 1.99 Å. The Fe(2)-O(20) bond length is 1.96 Å. The Fe(2)-O(23) bond length is 2.05 Å. The Fe(2)-O(4) bond length is 2.02 Å. The Fe(2)-O(8) bond length is 1.97 Å. In the third Fe site, Fe(3) is bonded to one O(10), one O(13), one O(21), one O(25), one O(5), and one O(6) atom to form distorted FeO6 trigonal bipyramids that share  a cornercorner with one Fe(2)O6 octahedra,  a cornercorner with one P(5)O4 tetrahedra,  a cornercorner with one P(6)O4 tetrahedra,  a cornercorner with one P(7)O4 tetrahedra,  a cornercorner with one P(8)O4 tetrahedra, and  an edgeedge with one P(4)O4 tetrahedra. The corner-sharing octahedral tilt angles are 57°. The Fe(3)-O(10) bond length is 2.57 Å. The Fe(3)-O(13) bond length is 1.95 Å. The Fe(3)-O(21) bond length is 1.88 Å. The Fe(3)-O(25) bond length is 2.02 Å. The Fe(3)-O(5) bond length is 1.97 Å. The Fe(3)-O(6) bond length is 1.99 Å. In the fourth Fe site, Fe(4) is bonded to one O(1), one O(11), one O(15), one O(2), one O(22), and one O(9) atom to form distorted FeO6 trigonal bipyramids that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one P(2)O4 tetrahedra,  a cornercorner with one P(3)O4 tetrahedra,  a cornercorner with one P(5)O4 tetrahedra,  a cornercorner with one P(8)O4 tetrahedra, and  an edgeedge with one P(1)O4 tetrahedra. The corner-sharing octahedral tilt angles are 57°. The Fe(4)-O(1) bond length is 2.57 Å. The Fe(4)-O(11) bond length is 1.95 Å. The Fe(4)-O(15) bond length is 1.99 Å. The Fe(4)-O(2) bond length is 1.94 Å. The Fe(4)-O(22) bond length is 2.02 Å. The Fe(4)-O(9) bond length is 1.88 Å. There are eight inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(19), one O(22), and one O(8) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one Fe(2)O6 octahedra,  a cornercorner with one P(7)O4 tetrahedra, and  an edgeedge with one Fe(4)O6 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 43-46°. The P(1)-O(1) bond length is 1.55 Å. The P(1)-O(19) bond length is 1.56 Å. The P(1)-O(22) bond length is 1.54 Å. The P(1)-O(8) bond length is 1.52 Å. In the second P site, P(2) is bonded to one O(16), one O(27), one O(28), and one O(9) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one P(8)O4 tetrahedra, and  a cornercorner with one Fe(4)O6 trigonal bipyramid. The corner-sharing octahedral tilt angles are 41°. The P(2)-O(16) bond length is 1.61 Å. The P(2)-O(27) bond length is 1.56 Å. The P(2)-O(28) bond length is 1.54 Å. The P(2)-O(9) bond length is 1.53 Å. In the third P site, P(3) is bonded to one O(14), one O(15), one O(24), and one O(3) atom to form PO4 tetrahedra that share corners with two equivalent Fe(1)O6 octahedra,  a cornercorner with one P(4)O4 tetrahedra, and  a cornercorner with one Fe(4)O6 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 31-49°. The P(3)-O(14) bond length is 1.54 Å. The P(3)-O(15) bond length is 1.59 Å. The P(3)-O(24) bond length is 1.50 Å. The P(3)-O(3) bond length is 1.61 Å. In the fourth P site, P(4) is bonded to one O(10), one O(17), one O(25), and one O(3) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one Fe(2)O6 octahedra,  a cornercorner with one P(3)O4 tetrahedra, and  an edgeedge with one Fe(3)O6 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 43-46°. The P(4)-O(10) bond length is 1.55 Å. The P(4)-O(17) bond length is 1.52 Å. The P(4)-O(25) bond length is 1.54 Å. The P(4)-O(3) bond length is 1.56 Å. In the fifth P site, P(5) is bonded to one O(11), one O(18), one O(5), and one O(7) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one P(6)O4 tetrahedra,  a cornercorner with one Fe(3)O6 trigonal bipyramid, and  a cornercorner with one Fe(4)O6 trigonal bipyramid. The corner-sharing octahedral tilt angles are 38°. The P(5)-O(11) bond length is 1.53 Å. The P(5)-O(18) bond length is 1.62 Å. The P(5)-O(5) bond length is 1.52 Å. The P(5)-O(7) bond length is 1.52 Å. In the sixth P site, P(6) is bonded to one O(18), one O(20), one O(21), and one O(26) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra,  a cornercorner with one P(5)O4 tetrahedra, and  a cornercorner with one Fe(3)O6 trigonal bipyramid. The corner-sharing octahedral tilt angles are 41°. The P(6)-O(18) bond length is 1.61 Å. The P(6)-O(20) bond length is 1.56 Å. The P(6)-O(21) bond length is 1.53 Å. The P(6)-O(26) bond length is 1.52 Å. In the seventh P site, P(7) is bonded to one O(19), one O(23), one O(4), and one O(6) atom to form PO4 tetrahedra that share corners with two equivalent Fe(2)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra, and  a cornercorner with one Fe(3)O6 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 31-49°. The P(7)-O(19) bond length is 1.61 Å. The P(7)-O(23) bond length is 1.50 Å. The P(7)-O(4) bond length is 1.54 Å. The P(7)-O(6) bond length is 1.59 Å. In the eighth P site, P(8) is bonded to one O(12), one O(13), one O(16), and one O(2) atom to form PO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra,  a cornercorner with one P(2)O4 tetrahedra,  a cornercorner with one Fe(3)O6 trigonal bipyramid, and  a cornercorner with one Fe(4)O6 trigonal bipyramid. The corner-sharing octahedral tilt angles are 38°. The P(8)-O(12) bond length is 1.52 Å. The P(8)-O(13) bond length is 1.53 Å. The P(8)-O(16) bond length is 1.62 Å. The P(8)-O(2) bond length is 1.57 Å. There are twenty-eight inequivalent O sites. In the first O site, O(1) is bonded in a 2-coordinate geometry to one Fe(1), one Fe(4), and one P(1) atom. In the second O site, O(2) is bonded in a distorted bent 150 degrees geometry to one Fe(4) and one P(8) atom. In the third O site, O(3) is bonded in a bent 120 degrees geometry to one P(3) and one P(4) atom. In the fourth O site, O(4) is bonded in a distorted bent 120 degrees geometry to one Fe(2) and one P(7) atom. In the fifth O site, O(5) is bonded in a distorted bent 150 degrees geometry to one Fe(3) and one P(5) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one Fe(3) and one P(7) atom. In the seventh O site, O(7) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(5) atom. In the eighth O site, O(8) is bonded in a distorted bent 120 degrees geometry to one Fe(2) and one P(1) atom. In the ninth O site, O(9) is bonded in a bent 150 degrees geometry to one Fe(4) and one P(2) atom. In the tenth O site, O(10) is bonded in a 2-coordinate geometry to one Fe(2), one Fe(3), and one P(4) atom. In the eleventh O site, O(11) is bonded in a bent 150 degrees geometry to one Fe(4) and one P(5) atom. In the twelfth O site, O(12) is bonded in a bent 150 degrees geometry to one Fe(2) and one P(8) atom. In the thirteenth O site, O(13) is bonded in a bent 150 degrees geometry to one Fe(3) and one P(8) atom. In the fourteenth O site, O(14) is bonded in a distorted bent 120 degrees geometry to one Fe(1) and one P(3) atom. In the fifteenth O site, O(15) is bonded in a bent 150 degrees geometry to one Fe(4) and one P(3) atom. In the sixteenth O site, O(16) is bonded in a distorted bent 120 degrees geometry to one P(2) and one P(8) atom. In the seventeenth O site, O(17) is bonded in a distorted bent 120 degrees geometry to one Fe(1) and one P(4) atom. In the eighteenth O site, O(18) is bonded in a distorted bent 120 degrees geometry to one P(5) and one P(6) atom. In the nineteenth O site, O(19) is bonded in a bent 120 degrees geometry to one P(1) and one P(7) atom. In the twentieth O site, O(20) is bonded in a bent 150 degrees geometry to one Fe(2) and one P(6) atom. In the twenty-first O site, O(21) is bonded in a bent 150 degrees geometry to one Fe(3) and one P(6) atom. In the twenty-second O site, O(22) is bonded in a water-like geometry to one Fe(4) and one P(1) atom. In the twenty-third O site, O(23) is bonded in a bent 150 degrees geometry to one Fe(2) and one P(7) atom. In the twenty-fourth O site, O(24) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(3) atom. In the twenty-fifth O site, O(25) is bonded in a water-like geometry to one Fe(3) and one P(4) atom. In the twenty-sixth O site, O(26) is bonded in a single-bond geometry to one P(6) atom. In the twenty-seventh O site, O(27) is bonded in a bent 150 degrees geometry to one Fe(1) and one P(2) atom. In the twenty-eighth O site, O(28) is bonded in a single-bond geometry to one P(2) atom.