RbMgFe(MoO4)2 crystallizes in the trigonal P3 space group. Rb(1) is bonded to three equivalent O(1), three equivalent O(2), three equivalent O(3), and three equivalent O(4) atoms to form RbO12 cuboctahedra that share edges with six equivalent Rb(1)O12 cuboctahedra, edges with three equivalent Mg(1)O4 tetrahedra, edges with three equivalent Mo(1)O4 tetrahedra, edges with three equivalent Mo(2)O4 tetrahedra, and faces with two equivalent Fe(1)O6 octahedra. Mg(1) is bonded to one O(4) and three equivalent O(1) atoms to form MgO4 tetrahedra that share corners with three equivalent Fe(1)O6 octahedra,  a cornercorner with one Mo(1)O4 tetrahedra, corners with three equivalent Mo(2)O4 tetrahedra, and edges with three equivalent Rb(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 53°. There are two inequivalent Mo sites. In the first Mo site, Mo(1) is bonded to one O(4) and three equivalent O(2) atoms to form MoO4 tetrahedra that share corners with three equivalent Fe(1)O6 octahedra,  a cornercorner with one Mg(1)O4 tetrahedra, and edges with three equivalent Rb(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 33°. In the second Mo site, Mo(2) is bonded to one O(3) and three equivalent O(1) atoms to form MoO4 tetrahedra that share corners with three equivalent Fe(1)O6 octahedra, corners with three equivalent Mg(1)O4 tetrahedra, and edges with three equivalent Rb(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 52°. Fe(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form FeO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, corners with three equivalent Mo(1)O4 tetrahedra, corners with three equivalent Mo(2)O4 tetrahedra, and faces with two equivalent Rb(1)O12 cuboctahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Rb(1), one Mg(1), one Mo(2), and one Fe(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Rb(1), one Mo(1), and one Fe(1) atom. In the third O site, O(3) is bonded in a single-bond geometry to three equivalent Rb(1) and one Mo(2) atom. In the fourth O site, O(4) is bonded in a linear geometry to three equivalent Rb(1), one Mg(1), and one Mo(1) atom.
RbMgFe(MoO4)2 crystallizes in the trigonal P3 space group. Rb(1) is bonded to three equivalent O(1), three equivalent O(2), three equivalent O(3), and three equivalent O(4) atoms to form RbO12 cuboctahedra that share edges with six equivalent Rb(1)O12 cuboctahedra, edges with three equivalent Mg(1)O4 tetrahedra, edges with three equivalent Mo(1)O4 tetrahedra, edges with three equivalent Mo(2)O4 tetrahedra, and faces with two equivalent Fe(1)O6 octahedra. All Rb(1)-O(1) bond lengths are 3.10 Å. All Rb(1)-O(2) bond lengths are 2.91 Å. All Rb(1)-O(3) bond lengths are 3.20 Å. All Rb(1)-O(4) bond lengths are 3.20 Å. Mg(1) is bonded to one O(4) and three equivalent O(1) atoms to form MgO4 tetrahedra that share corners with three equivalent Fe(1)O6 octahedra,  a cornercorner with one Mo(1)O4 tetrahedra, corners with three equivalent Mo(2)O4 tetrahedra, and edges with three equivalent Rb(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 53°. The Mg(1)-O(4) bond length is 2.06 Å. All Mg(1)-O(1) bond lengths are 1.99 Å. There are two inequivalent Mo sites. In the first Mo site, Mo(1) is bonded to one O(4) and three equivalent O(2) atoms to form MoO4 tetrahedra that share corners with three equivalent Fe(1)O6 octahedra,  a cornercorner with one Mg(1)O4 tetrahedra, and edges with three equivalent Rb(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 33°. The Mo(1)-O(4) bond length is 1.82 Å. All Mo(1)-O(2) bond lengths are 1.79 Å. In the second Mo site, Mo(2) is bonded to one O(3) and three equivalent O(1) atoms to form MoO4 tetrahedra that share corners with three equivalent Fe(1)O6 octahedra, corners with three equivalent Mg(1)O4 tetrahedra, and edges with three equivalent Rb(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles are 52°. The Mo(2)-O(3) bond length is 1.78 Å. All Mo(2)-O(1) bond lengths are 2.05 Å. Fe(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form FeO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, corners with three equivalent Mo(1)O4 tetrahedra, corners with three equivalent Mo(2)O4 tetrahedra, and faces with two equivalent Rb(1)O12 cuboctahedra. All Fe(1)-O(1) bond lengths are 1.99 Å. All Fe(1)-O(2) bond lengths are 2.15 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Rb(1), one Mg(1), one Mo(2), and one Fe(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Rb(1), one Mo(1), and one Fe(1) atom. In the third O site, O(3) is bonded in a single-bond geometry to three equivalent Rb(1) and one Mo(2) atom. In the fourth O site, O(4) is bonded in a linear geometry to three equivalent Rb(1), one Mg(1), and one Mo(1) atom.