Rb4Mg(FeO2)4 crystallizes in the triclinic P1 space group. There are four inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 4-coordinate geometry to one O(2), one O(4), one O(7), and one O(8) atom. In the second Rb site, Rb(2) is bonded in a 6-coordinate geometry to one O(5), one O(6), two equivalent O(1), and two equivalent O(3) atoms. In the third Rb site, Rb(3) is bonded in a 6-coordinate geometry to one O(2), one O(3), one O(4), one O(8), and two equivalent O(6) atoms. In the fourth Rb site, Rb(4) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(4), one O(7), and two equivalent O(5) atoms. Mg(1) is bonded in a 4-coordinate geometry to one O(1), one O(3), one O(7), and one O(8) atom. There are four inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(1), one O(3), one O(7), and one O(8) atom to form distorted corner-sharing FeO4 tetrahedra. In the second Fe site, Fe(2) is bonded to one O(2), one O(4), one O(5), and one O(6) atom to form distorted corner-sharing FeO4 trigonal pyramids. In the third Fe site, Fe(3) is bonded to one O(3), one O(4), one O(5), and one O(7) atom to form corner-sharing FeO4 tetrahedra. In the fourth Fe site, Fe(4) is bonded to one O(1), one O(2), one O(6), and one O(8) atom to form corner-sharing FeO4 tetrahedra. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to one Rb(4), two equivalent Rb(2), one Mg(1), one Fe(1), and one Fe(4) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Rb(1), one Rb(3), one Rb(4), one Fe(2), and one Fe(4) atom. In the third O site, O(3) is bonded in a 6-coordinate geometry to one Rb(3), two equivalent Rb(2), one Mg(1), one Fe(1), and one Fe(3) atom. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to one Rb(1), one Rb(3), one Rb(4), one Fe(2), and one Fe(3) atom. In the fifth O site, O(5) is bonded in a 5-coordinate geometry to one Rb(2), two equivalent Rb(4), one Fe(2), and one Fe(3) atom. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to one Rb(2), two equivalent Rb(3), one Fe(2), and one Fe(4) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Rb(1), one Rb(4), one Mg(1), one Fe(1), and one Fe(3) atom. In the eighth O site, O(8) is bonded in a 5-coordinate geometry to one Rb(1), one Rb(3), one Mg(1), one Fe(1), and one Fe(4) atom.
Rb4Mg(FeO2)4 crystallizes in the triclinic P1 space group. There are four inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 4-coordinate geometry to one O(2), one O(4), one O(7), and one O(8) atom. The Rb(1)-O(2) bond length is 3.04 Å. The Rb(1)-O(4) bond length is 2.95 Å. The Rb(1)-O(7) bond length is 3.04 Å. The Rb(1)-O(8) bond length is 3.01 Å. In the second Rb site, Rb(2) is bonded in a 6-coordinate geometry to one O(5), one O(6), two equivalent O(1), and two equivalent O(3) atoms. The Rb(2)-O(5) bond length is 2.86 Å. The Rb(2)-O(6) bond length is 3.01 Å. There is one shorter (2.85 Å) and one longer (3.05 Å) Rb(2)-O(1) bond length. There is one shorter (2.86 Å) and one longer (3.07 Å) Rb(2)-O(3) bond length. In the third Rb site, Rb(3) is bonded in a 6-coordinate geometry to one O(2), one O(3), one O(4), one O(8), and two equivalent O(6) atoms. The Rb(3)-O(2) bond length is 2.84 Å. The Rb(3)-O(3) bond length is 3.10 Å. The Rb(3)-O(4) bond length is 2.82 Å. The Rb(3)-O(8) bond length is 2.89 Å. There is one shorter (2.97 Å) and one longer (3.12 Å) Rb(3)-O(6) bond length. In the fourth Rb site, Rb(4) is bonded in a 6-coordinate geometry to one O(1), one O(2), one O(4), one O(7), and two equivalent O(5) atoms. The Rb(4)-O(1) bond length is 3.01 Å. The Rb(4)-O(2) bond length is 2.88 Å. The Rb(4)-O(4) bond length is 3.05 Å. The Rb(4)-O(7) bond length is 2.95 Å. There is one shorter (2.97 Å) and one longer (3.05 Å) Rb(4)-O(5) bond length. Mg(1) is bonded in a 4-coordinate geometry to one O(1), one O(3), one O(7), and one O(8) atom. The Mg(1)-O(1) bond length is 2.11 Å. The Mg(1)-O(3) bond length is 2.07 Å. The Mg(1)-O(7) bond length is 1.96 Å. The Mg(1)-O(8) bond length is 1.96 Å. There are four inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(1), one O(3), one O(7), and one O(8) atom to form distorted corner-sharing FeO4 tetrahedra. The Fe(1)-O(1) bond length is 2.05 Å. The Fe(1)-O(3) bond length is 2.07 Å. The Fe(1)-O(7) bond length is 2.15 Å. The Fe(1)-O(8) bond length is 2.20 Å. In the second Fe site, Fe(2) is bonded to one O(2), one O(4), one O(5), and one O(6) atom to form distorted corner-sharing FeO4 trigonal pyramids. The Fe(2)-O(2) bond length is 2.07 Å. The Fe(2)-O(4) bond length is 2.06 Å. The Fe(2)-O(5) bond length is 2.01 Å. The Fe(2)-O(6) bond length is 2.02 Å. In the third Fe site, Fe(3) is bonded to one O(3), one O(4), one O(5), and one O(7) atom to form corner-sharing FeO4 tetrahedra. The Fe(3)-O(3) bond length is 2.03 Å. The Fe(3)-O(4) bond length is 1.87 Å. The Fe(3)-O(5) bond length is 1.85 Å. The Fe(3)-O(7) bond length is 1.98 Å. In the fourth Fe site, Fe(4) is bonded to one O(1), one O(2), one O(6), and one O(8) atom to form corner-sharing FeO4 tetrahedra. The Fe(4)-O(1) bond length is 2.03 Å. The Fe(4)-O(2) bond length is 1.85 Å. The Fe(4)-O(6) bond length is 1.87 Å. The Fe(4)-O(8) bond length is 2.00 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to one Rb(4), two equivalent Rb(2), one Mg(1), one Fe(1), and one Fe(4) atom. In the second O site, O(2) is bonded in a 2-coordinate geometry to one Rb(1), one Rb(3), one Rb(4), one Fe(2), and one Fe(4) atom. In the third O site, O(3) is bonded in a 6-coordinate geometry to one Rb(3), two equivalent Rb(2), one Mg(1), one Fe(1), and one Fe(3) atom. In the fourth O site, O(4) is bonded in a 2-coordinate geometry to one Rb(1), one Rb(3), one Rb(4), one Fe(2), and one Fe(3) atom. In the fifth O site, O(5) is bonded in a 5-coordinate geometry to one Rb(2), two equivalent Rb(4), one Fe(2), and one Fe(3) atom. In the sixth O site, O(6) is bonded in a 2-coordinate geometry to one Rb(2), two equivalent Rb(3), one Fe(2), and one Fe(4) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Rb(1), one Rb(4), one Mg(1), one Fe(1), and one Fe(3) atom. In the eighth O site, O(8) is bonded in a 5-coordinate geometry to one Rb(1), one Rb(3), one Mg(1), one Fe(1), and one Fe(4) atom.