KFe3(SO7)2 crystallizes in the trigonal R3m space group. K(1) is bonded to three equivalent O(3), three equivalent O(4), three equivalent O(5), and three equivalent O(6) atoms to form KO12 cuboctahedra that share corners with three equivalent S(1)O4 tetrahedra, corners with three equivalent S(2)O4 tetrahedra, and faces with six equivalent Fe(1)O6 octahedra. Fe(1) is bonded to one O(3), one O(4), two equivalent O(5), and two equivalent O(6) atoms to form FeO6 octahedra that share corners with four equivalent Fe(1)O6 octahedra,  a cornercorner with one S(1)O4 tetrahedra,  a cornercorner with one S(2)O4 tetrahedra, and faces with two equivalent K(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 40-46°. There are two inequivalent S sites. In the first S site, S(1) is bonded to one O(1) and three equivalent O(3) atoms to form SO4 tetrahedra that share corners with three equivalent K(1)O12 cuboctahedra and corners with three equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. In the second S site, S(2) is bonded to one O(2) and three equivalent O(4) atoms to form SO4 tetrahedra that share corners with three equivalent K(1)O12 cuboctahedra and corners with three equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles are 55°. There are six inequivalent O sites. In the first O site, O(1) is bonded in a single-bond geometry to one S(1) atom. In the second O site, O(2) is bonded in a single-bond geometry to one S(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one K(1), one Fe(1), and one S(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one K(1), one Fe(1), and one S(2) atom. In the fifth O site, O(5) is bonded in a distorted bent 150 degrees geometry to one K(1) and two equivalent Fe(1) atoms. In the sixth O site, O(6) is bonded in a distorted bent 120 degrees geometry to one K(1) and two equivalent Fe(1) atoms.
KFe3(SO7)2 crystallizes in the trigonal R3m space group. K(1) is bonded to three equivalent O(3), three equivalent O(4), three equivalent O(5), and three equivalent O(6) atoms to form KO12 cuboctahedra that share corners with three equivalent S(1)O4 tetrahedra, corners with three equivalent S(2)O4 tetrahedra, and faces with six equivalent Fe(1)O6 octahedra. All K(1)-O(3) bond lengths are 2.89 Å. All K(1)-O(4) bond lengths are 2.91 Å. All K(1)-O(5) bond lengths are 3.04 Å. All K(1)-O(6) bond lengths are 3.18 Å. Fe(1) is bonded to one O(3), one O(4), two equivalent O(5), and two equivalent O(6) atoms to form FeO6 octahedra that share corners with four equivalent Fe(1)O6 octahedra,  a cornercorner with one S(1)O4 tetrahedra,  a cornercorner with one S(2)O4 tetrahedra, and faces with two equivalent K(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 40-46°. The Fe(1)-O(3) bond length is 2.08 Å. The Fe(1)-O(4) bond length is 2.11 Å. Both Fe(1)-O(5) bond lengths are 1.92 Å. Both Fe(1)-O(6) bond lengths are 1.84 Å. There are two inequivalent S sites. In the first S site, S(1) is bonded to one O(1) and three equivalent O(3) atoms to form SO4 tetrahedra that share corners with three equivalent K(1)O12 cuboctahedra and corners with three equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. The S(1)-O(1) bond length is 1.45 Å. All S(1)-O(3) bond lengths are 1.51 Å. In the second S site, S(2) is bonded to one O(2) and three equivalent O(4) atoms to form SO4 tetrahedra that share corners with three equivalent K(1)O12 cuboctahedra and corners with three equivalent Fe(1)O6 octahedra. The corner-sharing octahedral tilt angles are 55°. The S(2)-O(2) bond length is 1.45 Å. All S(2)-O(4) bond lengths are 1.50 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a single-bond geometry to one S(1) atom. In the second O site, O(2) is bonded in a single-bond geometry to one S(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one K(1), one Fe(1), and one S(1) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one K(1), one Fe(1), and one S(2) atom. In the fifth O site, O(5) is bonded in a distorted bent 150 degrees geometry to one K(1) and two equivalent Fe(1) atoms. In the sixth O site, O(6) is bonded in a distorted bent 120 degrees geometry to one K(1) and two equivalent Fe(1) atoms.