K2Mg(FeO2)2 crystallizes in the triclinic P1 space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 6-coordinate geometry to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. In the second K site, K(2) is bonded in a 5-coordinate geometry to one O(3), two equivalent O(1), and two equivalent O(2) atoms. Mg(1) is bonded to one O(2), one O(4), and two equivalent O(1) atoms to form MgO4 tetrahedra that share corners with two equivalent Mg(1)O4 tetrahedra, corners with three equivalent Fe(1)O4 tetrahedra,  a cornercorner with one Fe(2)O4 trigonal pyramid, and edges with two equivalent Fe(2)O4 trigonal pyramids. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(1), one O(4), and two equivalent O(3) atoms to form FeO4 tetrahedra that share corners with two equivalent Fe(1)O4 tetrahedra, corners with three equivalent Mg(1)O4 tetrahedra, and  an edgeedge with one Fe(2)O4 trigonal pyramid. In the second Fe site, Fe(2) is bonded to one O(1), one O(4), and two equivalent O(2) atoms to form distorted FeO4 trigonal pyramids that share  a cornercorner with one Mg(1)O4 tetrahedra, corners with two equivalent Fe(2)O4 trigonal pyramids,  an edgeedge with one Fe(1)O4 tetrahedra, and edges with two equivalent Mg(1)O4 tetrahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to two equivalent K(2), two equivalent Mg(1), one Fe(1), and one Fe(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to two equivalent K(1), two equivalent K(2), one Mg(1), and two equivalent Fe(2) atoms. In the third O site, O(3) is bonded in a 5-coordinate geometry to one K(2), two equivalent K(1), and two equivalent Fe(1) atoms. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to two equivalent K(1), one Mg(1), one Fe(1), and one Fe(2) atom.
K2Mg(FeO2)2 crystallizes in the triclinic P1 space group. There are two inequivalent K sites. In the first K site, K(1) is bonded in a 6-coordinate geometry to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. There is one shorter (2.89 Å) and one longer (2.97 Å) K(1)-O(2) bond length. There is one shorter (2.77 Å) and one longer (2.78 Å) K(1)-O(3) bond length. There is one shorter (2.77 Å) and one longer (2.83 Å) K(1)-O(4) bond length. In the second K site, K(2) is bonded in a 5-coordinate geometry to one O(3), two equivalent O(1), and two equivalent O(2) atoms. The K(2)-O(3) bond length is 2.78 Å. There is one shorter (2.86 Å) and one longer (2.90 Å) K(2)-O(1) bond length. There is one shorter (2.95 Å) and one longer (3.03 Å) K(2)-O(2) bond length. Mg(1) is bonded to one O(2), one O(4), and two equivalent O(1) atoms to form MgO4 tetrahedra that share corners with two equivalent Mg(1)O4 tetrahedra, corners with three equivalent Fe(1)O4 tetrahedra,  a cornercorner with one Fe(2)O4 trigonal pyramid, and edges with two equivalent Fe(2)O4 trigonal pyramids. The Mg(1)-O(2) bond length is 2.09 Å. The Mg(1)-O(4) bond length is 1.94 Å. There is one shorter (2.00 Å) and one longer (2.02 Å) Mg(1)-O(1) bond length. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(1), one O(4), and two equivalent O(3) atoms to form FeO4 tetrahedra that share corners with two equivalent Fe(1)O4 tetrahedra, corners with three equivalent Mg(1)O4 tetrahedra, and  an edgeedge with one Fe(2)O4 trigonal pyramid. The Fe(1)-O(1) bond length is 2.24 Å. The Fe(1)-O(4) bond length is 2.15 Å. Both Fe(1)-O(3) bond lengths are 1.99 Å. In the second Fe site, Fe(2) is bonded to one O(1), one O(4), and two equivalent O(2) atoms to form distorted FeO4 trigonal pyramids that share  a cornercorner with one Mg(1)O4 tetrahedra, corners with two equivalent Fe(2)O4 trigonal pyramids,  an edgeedge with one Fe(1)O4 tetrahedra, and edges with two equivalent Mg(1)O4 tetrahedra. The Fe(2)-O(1) bond length is 2.18 Å. The Fe(2)-O(4) bond length is 1.92 Å. There is one shorter (2.01 Å) and one longer (2.15 Å) Fe(2)-O(2) bond length. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to two equivalent K(2), two equivalent Mg(1), one Fe(1), and one Fe(2) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to two equivalent K(1), two equivalent K(2), one Mg(1), and two equivalent Fe(2) atoms. In the third O site, O(3) is bonded in a 5-coordinate geometry to one K(2), two equivalent K(1), and two equivalent Fe(1) atoms. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to two equivalent K(1), one Mg(1), one Fe(1), and one Fe(2) atom.