RbMgMn4O8 crystallizes in the triclinic P1 space group. Rb(1) is bonded in a 5-coordinate geometry to one O(8), two equivalent O(5), and two equivalent O(7) atoms. Mg(1) is bonded in a distorted see-saw-like geometry to one O(2), one O(4), and two equivalent O(6) atoms. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(1), one O(2), one O(6), and two equivalent O(7) atoms to form distorted MnO5 trigonal bipyramids that share  a cornercorner with one Mn(3)O6 octahedra, corners with two equivalent Mn(2)O6 octahedra, corners with two equivalent Mn(1)O5 trigonal bipyramids, and edges with two equivalent Mn(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 24-58°. In the second Mn site, Mn(2) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(5) atoms to form MnO6 octahedra that share corners with two equivalent Mn(4)O6 octahedra, corners with two equivalent Mn(1)O5 trigonal bipyramids, edges with two equivalent Mn(2)O6 octahedra, and edges with two equivalent Mn(3)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. In the third Mn site, Mn(3) is bonded to one O(5), one O(6), two equivalent O(4), and two equivalent O(8) atoms to form distorted MnO6 octahedra that share corners with two equivalent Mn(4)O6 octahedra,  a cornercorner with one Mn(1)O5 trigonal bipyramid, edges with two equivalent Mn(2)O6 octahedra, and edges with two equivalent Mn(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 52-58°. In the fourth Mn site, Mn(4) is bonded to one O(7), one O(8), two equivalent O(2), and two equivalent O(3) atoms to form distorted MnO6 octahedra that share corners with two equivalent Mn(2)O6 octahedra, corners with two equivalent Mn(3)O6 octahedra, edges with two equivalent Mn(4)O6 octahedra, and edges with two equivalent Mn(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 51-58°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Mn(1) and two equivalent Mn(2) atoms. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Mg(1), one Mn(1), and two equivalent Mn(4) atoms. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Mn(2) and two equivalent Mn(4) atoms. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Mg(1), one Mn(2), and two equivalent Mn(3) atoms. In the fifth O site, O(5) is bonded in a 5-coordinate geometry to two equivalent Rb(1), one Mn(3), and two equivalent Mn(2) atoms. In the sixth O site, O(6) is bonded in a see-saw-like geometry to two equivalent Mg(1), one Mn(1), and one Mn(3) atom. In the seventh O site, O(7) is bonded in a 5-coordinate geometry to two equivalent Rb(1), one Mn(4), and two equivalent Mn(1) atoms. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Rb(1), one Mn(4), and two equivalent Mn(3) atoms.
RbMgMn4O8 crystallizes in the triclinic P1 space group. Rb(1) is bonded in a 5-coordinate geometry to one O(8), two equivalent O(5), and two equivalent O(7) atoms. The Rb(1)-O(8) bond length is 3.03 Å. There is one shorter (2.70 Å) and one longer (2.82 Å) Rb(1)-O(5) bond length. There is one shorter (2.75 Å) and one longer (2.85 Å) Rb(1)-O(7) bond length. Mg(1) is bonded in a distorted see-saw-like geometry to one O(2), one O(4), and two equivalent O(6) atoms. The Mg(1)-O(2) bond length is 1.96 Å. The Mg(1)-O(4) bond length is 1.90 Å. There is one shorter (1.94 Å) and one longer (1.99 Å) Mg(1)-O(6) bond length. There are four inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(1), one O(2), one O(6), and two equivalent O(7) atoms to form distorted MnO5 trigonal bipyramids that share  a cornercorner with one Mn(3)O6 octahedra, corners with two equivalent Mn(2)O6 octahedra, corners with two equivalent Mn(1)O5 trigonal bipyramids, and edges with two equivalent Mn(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 24-58°. The Mn(1)-O(1) bond length is 1.90 Å. The Mn(1)-O(2) bond length is 2.06 Å. The Mn(1)-O(6) bond length is 2.02 Å. There is one shorter (1.94 Å) and one longer (2.07 Å) Mn(1)-O(7) bond length. In the second Mn site, Mn(2) is bonded to one O(3), one O(4), two equivalent O(1), and two equivalent O(5) atoms to form MnO6 octahedra that share corners with two equivalent Mn(4)O6 octahedra, corners with two equivalent Mn(1)O5 trigonal bipyramids, edges with two equivalent Mn(2)O6 octahedra, and edges with two equivalent Mn(3)O6 octahedra. The corner-sharing octahedral tilt angles are 51°. The Mn(2)-O(3) bond length is 1.93 Å. The Mn(2)-O(4) bond length is 2.00 Å. There is one shorter (2.00 Å) and one longer (2.04 Å) Mn(2)-O(1) bond length. There is one shorter (2.05 Å) and one longer (2.08 Å) Mn(2)-O(5) bond length. In the third Mn site, Mn(3) is bonded to one O(5), one O(6), two equivalent O(4), and two equivalent O(8) atoms to form distorted MnO6 octahedra that share corners with two equivalent Mn(4)O6 octahedra,  a cornercorner with one Mn(1)O5 trigonal bipyramid, edges with two equivalent Mn(2)O6 octahedra, and edges with two equivalent Mn(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 52-58°. The Mn(3)-O(5) bond length is 2.00 Å. The Mn(3)-O(6) bond length is 2.06 Å. There is one shorter (2.01 Å) and one longer (2.39 Å) Mn(3)-O(4) bond length. There is one shorter (1.91 Å) and one longer (2.15 Å) Mn(3)-O(8) bond length. In the fourth Mn site, Mn(4) is bonded to one O(7), one O(8), two equivalent O(2), and two equivalent O(3) atoms to form distorted MnO6 octahedra that share corners with two equivalent Mn(2)O6 octahedra, corners with two equivalent Mn(3)O6 octahedra, edges with two equivalent Mn(4)O6 octahedra, and edges with two equivalent Mn(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 51-58°. The Mn(4)-O(7) bond length is 2.08 Å. The Mn(4)-O(8) bond length is 1.99 Å. There is one shorter (1.99 Å) and one longer (2.42 Å) Mn(4)-O(2) bond length. There is one shorter (1.95 Å) and one longer (2.14 Å) Mn(4)-O(3) bond length. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Mn(1) and two equivalent Mn(2) atoms. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Mg(1), one Mn(1), and two equivalent Mn(4) atoms. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Mn(2) and two equivalent Mn(4) atoms. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Mg(1), one Mn(2), and two equivalent Mn(3) atoms. In the fifth O site, O(5) is bonded in a 5-coordinate geometry to two equivalent Rb(1), one Mn(3), and two equivalent Mn(2) atoms. In the sixth O site, O(6) is bonded in a see-saw-like geometry to two equivalent Mg(1), one Mn(1), and one Mn(3) atom. In the seventh O site, O(7) is bonded in a 5-coordinate geometry to two equivalent Rb(1), one Mn(4), and two equivalent Mn(1) atoms. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Rb(1), one Mn(4), and two equivalent Mn(3) atoms.