KFeAs2O7 crystallizes in the triclinic P-1 space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 10-coordinate geometry to one O(11), one O(12), one O(2), one O(3), one O(4), one O(5), one O(6), one O(9), and two equivalent O(14) atoms. In the second K site, K(2) is bonded in a 7-coordinate geometry to one O(1), one O(11), one O(12), one O(6), one O(7), and two equivalent O(10) atoms. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(12), one O(14), one O(3), one O(4), one O(6), and one O(8) atom to form FeO6 octahedra that share  a cornercorner with one As(1)O4 tetrahedra,  a cornercorner with one As(3)O4 tetrahedra, corners with two equivalent As(2)O4 tetrahedra, and corners with two equivalent As(4)O4 tetrahedra. In the second Fe site, Fe(2) is bonded to one O(1), one O(10), one O(11), one O(2), one O(5), and one O(7) atom to form FeO6 octahedra that share  a cornercorner with one As(2)O4 tetrahedra,  a cornercorner with one As(4)O4 tetrahedra, corners with two equivalent As(1)O4 tetrahedra, and corners with two equivalent As(3)O4 tetrahedra. There are four inequivalent As sites. In the first As site, As(1) is bonded to one O(10), one O(13), one O(2), and one O(6) atom to form AsO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra, and  a cornercorner with one As(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 34-55°. In the second As site, As(2) is bonded to one O(12), one O(4), one O(7), and one O(9) atom to form AsO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, and  a cornercorner with one As(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 35-57°. In the third As site, As(3) is bonded to one O(1), one O(13), one O(3), and one O(5) atom to form AsO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra, and  a cornercorner with one As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 31-53°. In the fourth As site, As(4) is bonded to one O(11), one O(14), one O(8), and one O(9) atom to form AsO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, and  a cornercorner with one As(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 39-52°. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one K(2), one Fe(2), and one As(3) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one K(1), one Fe(2), and one As(1) atom. In the third O site, O(3) is bonded in a distorted bent 120 degrees geometry to one K(1), one Fe(1), and one As(3) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one K(1), one Fe(1), and one As(2) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one K(1), one Fe(2), and one As(3) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one K(1), one K(2), one Fe(1), and one As(1) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one K(2), one Fe(2), and one As(2) atom. In the eighth O site, O(8) is bonded in a bent 150 degrees geometry to one Fe(1) and one As(4) atom. In the ninth O site, O(9) is bonded in a bent 120 degrees geometry to one K(1), one As(2), and one As(4) atom. In the tenth O site, O(10) is bonded in a 4-coordinate geometry to two equivalent K(2), one Fe(2), and one As(1) atom. In the eleventh O site, O(11) is bonded in a 2-coordinate geometry to one K(1), one K(2), one Fe(2), and one As(4) atom. In the twelfth O site, O(12) is bonded in a 2-coordinate geometry to one K(1), one K(2), one Fe(1), and one As(2) atom. In the thirteenth O site, O(13) is bonded in a bent 120 degrees geometry to one As(1) and one As(3) atom. In the fourteenth O site, O(14) is bonded in a 4-coordinate geometry to two equivalent K(1), one Fe(1), and one As(4) atom.
KFeAs2O7 crystallizes in the triclinic P-1 space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 10-coordinate geometry to one O(11), one O(12), one O(2), one O(3), one O(4), one O(5), one O(6), one O(9), and two equivalent O(14) atoms. The K(1)-O(11) bond length is 3.18 Å. The K(1)-O(12) bond length is 2.86 Å. The K(1)-O(2) bond length is 2.91 Å. The K(1)-O(3) bond length is 3.11 Å. The K(1)-O(4) bond length is 3.28 Å. The K(1)-O(5) bond length is 3.14 Å. The K(1)-O(6) bond length is 3.28 Å. The K(1)-O(9) bond length is 3.31 Å. There is one shorter (2.81 Å) and one longer (2.89 Å) K(1)-O(14) bond length. In the second K site, K(2) is bonded in a 7-coordinate geometry to one O(1), one O(11), one O(12), one O(6), one O(7), and two equivalent O(10) atoms. The K(2)-O(1) bond length is 2.90 Å. The K(2)-O(11) bond length is 2.86 Å. The K(2)-O(12) bond length is 3.30 Å. The K(2)-O(6) bond length is 2.76 Å. The K(2)-O(7) bond length is 2.88 Å. There is one shorter (2.79 Å) and one longer (3.05 Å) K(2)-O(10) bond length. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(12), one O(14), one O(3), one O(4), one O(6), and one O(8) atom to form FeO6 octahedra that share  a cornercorner with one As(1)O4 tetrahedra,  a cornercorner with one As(3)O4 tetrahedra, corners with two equivalent As(2)O4 tetrahedra, and corners with two equivalent As(4)O4 tetrahedra. The Fe(1)-O(12) bond length is 2.13 Å. The Fe(1)-O(14) bond length is 2.08 Å. The Fe(1)-O(3) bond length is 2.06 Å. The Fe(1)-O(4) bond length is 1.98 Å. The Fe(1)-O(6) bond length is 2.04 Å. The Fe(1)-O(8) bond length is 1.96 Å. In the second Fe site, Fe(2) is bonded to one O(1), one O(10), one O(11), one O(2), one O(5), and one O(7) atom to form FeO6 octahedra that share  a cornercorner with one As(2)O4 tetrahedra,  a cornercorner with one As(4)O4 tetrahedra, corners with two equivalent As(1)O4 tetrahedra, and corners with two equivalent As(3)O4 tetrahedra. The Fe(2)-O(1) bond length is 2.06 Å. The Fe(2)-O(10) bond length is 2.03 Å. The Fe(2)-O(11) bond length is 2.04 Å. The Fe(2)-O(2) bond length is 2.06 Å. The Fe(2)-O(5) bond length is 2.04 Å. The Fe(2)-O(7) bond length is 2.04 Å. There are four inequivalent As sites. In the first As site, As(1) is bonded to one O(10), one O(13), one O(2), and one O(6) atom to form AsO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra, and  a cornercorner with one As(3)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 34-55°. The As(1)-O(10) bond length is 1.71 Å. The As(1)-O(13) bond length is 1.79 Å. The As(1)-O(2) bond length is 1.69 Å. The As(1)-O(6) bond length is 1.72 Å. In the second As site, As(2) is bonded to one O(12), one O(4), one O(7), and one O(9) atom to form AsO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, and  a cornercorner with one As(4)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 35-57°. The As(2)-O(12) bond length is 1.70 Å. The As(2)-O(4) bond length is 1.70 Å. The As(2)-O(7) bond length is 1.72 Å. The As(2)-O(9) bond length is 1.80 Å. In the third As site, As(3) is bonded to one O(1), one O(13), one O(3), and one O(5) atom to form AsO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra, and  a cornercorner with one As(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 31-53°. The As(3)-O(1) bond length is 1.70 Å. The As(3)-O(13) bond length is 1.81 Å. The As(3)-O(3) bond length is 1.71 Å. The As(3)-O(5) bond length is 1.71 Å. In the fourth As site, As(4) is bonded to one O(11), one O(14), one O(8), and one O(9) atom to form AsO4 tetrahedra that share  a cornercorner with one Fe(2)O6 octahedra, corners with two equivalent Fe(1)O6 octahedra, and  a cornercorner with one As(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 39-52°. The As(4)-O(11) bond length is 1.70 Å. The As(4)-O(14) bond length is 1.70 Å. The As(4)-O(8) bond length is 1.69 Å. The As(4)-O(9) bond length is 1.80 Å. There are fourteen inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to one K(2), one Fe(2), and one As(3) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one K(1), one Fe(2), and one As(1) atom. In the third O site, O(3) is bonded in a distorted bent 120 degrees geometry to one K(1), one Fe(1), and one As(3) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one K(1), one Fe(1), and one As(2) atom. In the fifth O site, O(5) is bonded in a distorted bent 120 degrees geometry to one K(1), one Fe(2), and one As(3) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one K(1), one K(2), one Fe(1), and one As(1) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one K(2), one Fe(2), and one As(2) atom. In the eighth O site, O(8) is bonded in a bent 150 degrees geometry to one Fe(1) and one As(4) atom. In the ninth O site, O(9) is bonded in a bent 120 degrees geometry to one K(1), one As(2), and one As(4) atom. In the tenth O site, O(10) is bonded in a 4-coordinate geometry to two equivalent K(2), one Fe(2), and one As(1) atom. In the eleventh O site, O(11) is bonded in a 2-coordinate geometry to one K(1), one K(2), one Fe(2), and one As(4) atom. In the twelfth O site, O(12) is bonded in a 2-coordinate geometry to one K(1), one K(2), one Fe(1), and one As(2) atom. In the thirteenth O site, O(13) is bonded in a bent 120 degrees geometry to one As(1) and one As(3) atom. In the fourteenth O site, O(14) is bonded in a 4-coordinate geometry to two equivalent K(1), one Fe(1), and one As(4) atom.