K4MgMn4O8 crystallizes in the triclinic P1 space group. There are four inequivalent K sites. In the first K site, K(1) is bonded in a 5-coordinate geometry to one O(2), one O(3), one O(4), one O(5), and one O(8) atom. In the second K site, K(2) is bonded in a 5-coordinate geometry to one O(2), one O(3), one O(5), one O(6), and one O(8) atom. In the third K site, K(3) is bonded in a 5-coordinate geometry to one O(1), one O(2), one O(4), one O(6), and one O(7) atom. In the fourth K site, K(4) is bonded in a 5-coordinate geometry to one O(1), one O(4), one O(6), one O(7), and one O(8) atom. Mg(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form distorted MgO4 tetrahedra that share corners with two equivalent Mn(1)O5 square pyramids, corners with two equivalent Mn(2)O5 square pyramids, corners with two equivalent Mn(3)O5 square pyramids, and corners with two equivalent Mn(4)O5 square pyramids. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(2), one O(3), one O(5), one O(6), and one O(8) atom to form distorted MnO5 square pyramids that share corners with two equivalent Mg(1)O4 tetrahedra,  an edgeedge with one Mn(2)O5 square pyramid,  an edgeedge with one Mn(3)O5 square pyramid, and edges with two equivalent Mn(4)O5 square pyramids. In the second Mn site, Mn(2) is bonded to one O(1), one O(4), one O(5), one O(6), and one O(7) atom to form MnO5 square pyramids that share corners with two equivalent Mg(1)O4 tetrahedra,  an edgeedge with one Mn(1)O5 square pyramid,  an edgeedge with one Mn(4)O5 square pyramid, and edges with two equivalent Mn(3)O5 square pyramids. In the third Mn site, Mn(3) is bonded to one O(1), one O(4), one O(6), one O(7), and one O(8) atom to form distorted MnO5 square pyramids that share corners with two equivalent Mg(1)O4 tetrahedra,  an edgeedge with one Mn(1)O5 square pyramid,  an edgeedge with one Mn(4)O5 square pyramid, and edges with two equivalent Mn(2)O5 square pyramids. In the fourth Mn site, Mn(4) is bonded to one O(2), one O(3), one O(5), one O(7), and one O(8) atom to form MnO5 square pyramids that share corners with two equivalent Mg(1)O4 tetrahedra,  an edgeedge with one Mn(2)O5 square pyramid,  an edgeedge with one Mn(3)O5 square pyramid, and edges with two equivalent Mn(1)O5 square pyramids. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one K(3), one K(4), one Mg(1), one Mn(2), and one Mn(3) atom. In the second O site, O(2) is bonded in a 6-coordinate geometry to one K(1), one K(2), one K(3), one Mg(1), one Mn(1), and one Mn(4) atom. In the third O site, O(3) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Mg(1), one Mn(1), and one Mn(4) atom. In the fourth O site, O(4) is bonded in a 6-coordinate geometry to one K(1), one K(3), one K(4), one Mg(1), one Mn(2), and one Mn(3) atom. In the fifth O site, O(5) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Mn(1), one Mn(2), and one Mn(4) atom. In the sixth O site, O(6) is bonded in a 6-coordinate geometry to one K(2), one K(3), one K(4), one Mn(1), one Mn(2), and one Mn(3) atom. In the seventh O site, O(7) is bonded in a 5-coordinate geometry to one K(3), one K(4), one Mn(2), one Mn(3), and one Mn(4) atom. In the eighth O site, O(8) is bonded in a 6-coordinate geometry to one K(1), one K(2), one K(4), one Mn(1), one Mn(3), and one Mn(4) atom.
K4MgMn4O8 crystallizes in the triclinic P1 space group. There are four inequivalent K sites. In the first K site, K(1) is bonded in a 5-coordinate geometry to one O(2), one O(3), one O(4), one O(5), and one O(8) atom. The K(1)-O(2) bond length is 2.70 Å. The K(1)-O(3) bond length is 2.63 Å. The K(1)-O(4) bond length is 2.92 Å. The K(1)-O(5) bond length is 2.44 Å. The K(1)-O(8) bond length is 2.46 Å. In the second K site, K(2) is bonded in a 5-coordinate geometry to one O(2), one O(3), one O(5), one O(6), and one O(8) atom. The K(2)-O(2) bond length is 2.72 Å. The K(2)-O(3) bond length is 2.71 Å. The K(2)-O(5) bond length is 2.94 Å. The K(2)-O(6) bond length is 2.99 Å. The K(2)-O(8) bond length is 2.83 Å. In the third K site, K(3) is bonded in a 5-coordinate geometry to one O(1), one O(2), one O(4), one O(6), and one O(7) atom. The K(3)-O(1) bond length is 2.63 Å. The K(3)-O(2) bond length is 2.93 Å. The K(3)-O(4) bond length is 2.70 Å. The K(3)-O(6) bond length is 2.46 Å. The K(3)-O(7) bond length is 2.44 Å. In the fourth K site, K(4) is bonded in a 5-coordinate geometry to one O(1), one O(4), one O(6), one O(7), and one O(8) atom. The K(4)-O(1) bond length is 2.70 Å. The K(4)-O(4) bond length is 2.72 Å. The K(4)-O(6) bond length is 2.82 Å. The K(4)-O(7) bond length is 2.92 Å. The K(4)-O(8) bond length is 3.01 Å. Mg(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form distorted MgO4 tetrahedra that share corners with two equivalent Mn(1)O5 square pyramids, corners with two equivalent Mn(2)O5 square pyramids, corners with two equivalent Mn(3)O5 square pyramids, and corners with two equivalent Mn(4)O5 square pyramids. The Mg(1)-O(1) bond length is 1.99 Å. The Mg(1)-O(2) bond length is 2.11 Å. The Mg(1)-O(3) bond length is 1.99 Å. The Mg(1)-O(4) bond length is 2.11 Å. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(2), one O(3), one O(5), one O(6), and one O(8) atom to form distorted MnO5 square pyramids that share corners with two equivalent Mg(1)O4 tetrahedra,  an edgeedge with one Mn(2)O5 square pyramid,  an edgeedge with one Mn(3)O5 square pyramid, and edges with two equivalent Mn(4)O5 square pyramids. The Mn(1)-O(2) bond length is 2.21 Å. The Mn(1)-O(3) bond length is 2.11 Å. The Mn(1)-O(5) bond length is 2.28 Å. The Mn(1)-O(6) bond length is 2.19 Å. The Mn(1)-O(8) bond length is 2.25 Å. In the second Mn site, Mn(2) is bonded to one O(1), one O(4), one O(5), one O(6), and one O(7) atom to form MnO5 square pyramids that share corners with two equivalent Mg(1)O4 tetrahedra,  an edgeedge with one Mn(1)O5 square pyramid,  an edgeedge with one Mn(4)O5 square pyramid, and edges with two equivalent Mn(3)O5 square pyramids. The Mn(2)-O(1) bond length is 2.00 Å. The Mn(2)-O(4) bond length is 2.03 Å. The Mn(2)-O(5) bond length is 2.30 Å. The Mn(2)-O(6) bond length is 1.96 Å. The Mn(2)-O(7) bond length is 1.93 Å. In the third Mn site, Mn(3) is bonded to one O(1), one O(4), one O(6), one O(7), and one O(8) atom to form distorted MnO5 square pyramids that share corners with two equivalent Mg(1)O4 tetrahedra,  an edgeedge with one Mn(1)O5 square pyramid,  an edgeedge with one Mn(4)O5 square pyramid, and edges with two equivalent Mn(2)O5 square pyramids. The Mn(3)-O(1) bond length is 2.11 Å. The Mn(3)-O(4) bond length is 2.21 Å. The Mn(3)-O(6) bond length is 2.25 Å. The Mn(3)-O(7) bond length is 2.28 Å. The Mn(3)-O(8) bond length is 2.19 Å. In the fourth Mn site, Mn(4) is bonded to one O(2), one O(3), one O(5), one O(7), and one O(8) atom to form MnO5 square pyramids that share corners with two equivalent Mg(1)O4 tetrahedra,  an edgeedge with one Mn(2)O5 square pyramid,  an edgeedge with one Mn(3)O5 square pyramid, and edges with two equivalent Mn(1)O5 square pyramids. The Mn(4)-O(2) bond length is 2.03 Å. The Mn(4)-O(3) bond length is 2.00 Å. The Mn(4)-O(5) bond length is 1.93 Å. The Mn(4)-O(7) bond length is 2.31 Å. The Mn(4)-O(8) bond length is 1.96 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one K(3), one K(4), one Mg(1), one Mn(2), and one Mn(3) atom. In the second O site, O(2) is bonded in a 6-coordinate geometry to one K(1), one K(2), one K(3), one Mg(1), one Mn(1), and one Mn(4) atom. In the third O site, O(3) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Mg(1), one Mn(1), and one Mn(4) atom. In the fourth O site, O(4) is bonded in a 6-coordinate geometry to one K(1), one K(3), one K(4), one Mg(1), one Mn(2), and one Mn(3) atom. In the fifth O site, O(5) is bonded in a 5-coordinate geometry to one K(1), one K(2), one Mn(1), one Mn(2), and one Mn(4) atom. In the sixth O site, O(6) is bonded in a 6-coordinate geometry to one K(2), one K(3), one K(4), one Mn(1), one Mn(2), and one Mn(3) atom. In the seventh O site, O(7) is bonded in a 5-coordinate geometry to one K(3), one K(4), one Mn(2), one Mn(3), and one Mn(4) atom. In the eighth O site, O(8) is bonded in a 6-coordinate geometry to one K(1), one K(2), one K(4), one Mn(1), one Mn(3), and one Mn(4) atom.