MgCu2(RhO2)4 crystallizes in the triclinic P1 space group. Mg(1) is bonded in a 2-coordinate geometry to one O(1), one O(3), one O(5), and one O(8) atom. There are four inequivalent Rh sites. In the first Rh site, Rh(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(6), and one O(8) atom to form distorted RhO6 octahedra that share corners with three equivalent Cu(1)O4 tetrahedra, edges with two equivalent Rh(2)O6 octahedra, edges with two equivalent Rh(3)O6 octahedra, and edges with two equivalent Rh(4)O6 octahedra. In the second Rh site, Rh(2) is bonded to one O(2), one O(3), one O(4), one O(5), one O(7), and one O(8) atom to form distorted RhO6 octahedra that share corners with three equivalent Cu(1)O4 tetrahedra, edges with two equivalent Rh(1)O6 octahedra, edges with two equivalent Rh(3)O6 octahedra, and edges with two equivalent Rh(4)O6 octahedra. In the third Rh site, Rh(3) is bonded to one O(1), one O(2), one O(5), one O(6), one O(7), and one O(8) atom to form RhO6 octahedra that share corners with three equivalent Cu(1)O4 tetrahedra, edges with two equivalent Rh(1)O6 octahedra, edges with two equivalent Rh(2)O6 octahedra, and edges with two equivalent Rh(4)O6 octahedra. In the fourth Rh site, Rh(4) is bonded to one O(1), one O(3), one O(4), one O(5), one O(6), and one O(7) atom to form RhO6 octahedra that share corners with three equivalent Cu(1)O4 tetrahedra, edges with two equivalent Rh(1)O6 octahedra, edges with two equivalent Rh(2)O6 octahedra, and edges with two equivalent Rh(3)O6 octahedra. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(3), one O(6), one O(7), and one O(8) atom to form CuO4 tetrahedra that share corners with three equivalent Rh(1)O6 octahedra, corners with three equivalent Rh(2)O6 octahedra, corners with three equivalent Rh(3)O6 octahedra, and corners with three equivalent Rh(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 57-63°. In the second Cu site, Cu(2) is bonded in a distorted linear geometry to one O(2) and one O(4) atom. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Rh(1), one Rh(3), and one Rh(4) atom to form distorted OMgRh3 trigonal pyramids that share  a cornercorner with one O(8)MgCuRh3 trigonal bipyramid,  a cornercorner with one O(5)MgRh3 trigonal pyramid, corners with two equivalent O(7)CuRh3 trigonal pyramids,  an edgeedge with one O(8)MgCuRh3 trigonal bipyramid,  an edgeedge with one O(2)CuRh3 trigonal pyramid,  an edgeedge with one O(4)CuRh3 trigonal pyramid, and  an edgeedge with one O(5)MgRh3 trigonal pyramid. In the second O site, O(2) is bonded to one Rh(1), one Rh(2), one Rh(3), and one Cu(2) atom to form OCuRh3 trigonal pyramids that share corners with three equivalent O(8)MgCuRh3 trigonal bipyramids,  a cornercorner with one O(4)CuRh3 trigonal pyramid, corners with two equivalent O(7)CuRh3 trigonal pyramids,  an edgeedge with one O(4)CuRh3 trigonal pyramid,  an edgeedge with one O(1)MgRh3 trigonal pyramid, and  an edgeedge with one O(5)MgRh3 trigonal pyramid. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Mg(1), one Rh(1), one Rh(2), one Rh(4), and one Cu(1) atom. In the fourth O site, O(4) is bonded to one Rh(1), one Rh(2), one Rh(4), and one Cu(2) atom to form OCuRh3 trigonal pyramids that share corners with two equivalent O(8)MgCuRh3 trigonal bipyramids,  a cornercorner with one O(2)CuRh3 trigonal pyramid, corners with two equivalent O(7)CuRh3 trigonal pyramids,  an edgeedge with one O(2)CuRh3 trigonal pyramid,  an edgeedge with one O(1)MgRh3 trigonal pyramid, and  an edgeedge with one O(5)MgRh3 trigonal pyramid. In the fifth O site, O(5) is bonded to one Mg(1), one Rh(2), one Rh(3), and one Rh(4) atom to form distorted OMgRh3 trigonal pyramids that share  a cornercorner with one O(8)MgCuRh3 trigonal bipyramid,  a cornercorner with one O(1)MgRh3 trigonal pyramid, corners with three equivalent O(7)CuRh3 trigonal pyramids,  an edgeedge with one O(8)MgCuRh3 trigonal bipyramid,  an edgeedge with one O(2)CuRh3 trigonal pyramid,  an edgeedge with one O(4)CuRh3 trigonal pyramid, and  an edgeedge with one O(1)MgRh3 trigonal pyramid. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Rh(1), one Rh(3), one Rh(4), and one Cu(1) atom. In the seventh O site, O(7) is bonded to one Rh(2), one Rh(3), one Rh(4), and one Cu(1) atom to form distorted OCuRh3 trigonal pyramids that share  a cornercorner with one O(8)MgCuRh3 trigonal bipyramid, corners with two equivalent O(2)CuRh3 trigonal pyramids, corners with two equivalent O(4)CuRh3 trigonal pyramids, corners with two equivalent O(1)MgRh3 trigonal pyramids, corners with three equivalent O(5)MgRh3 trigonal pyramids, and  an edgeedge with one O(8)MgCuRh3 trigonal bipyramid. In the eighth O site, O(8) is bonded to one Mg(1), one Rh(1), one Rh(2), one Rh(3), and one Cu(1) atom to form distorted OMgCuRh3 trigonal bipyramids that share  a cornercorner with one O(7)CuRh3 trigonal pyramid,  a cornercorner with one O(1)MgRh3 trigonal pyramid,  a cornercorner with one O(5)MgRh3 trigonal pyramid, corners with two equivalent O(4)CuRh3 trigonal pyramids, corners with three equivalent O(2)CuRh3 trigonal pyramids,  an edgeedge with one O(7)CuRh3 trigonal pyramid,  an edgeedge with one O(1)MgRh3 trigonal pyramid, and  an edgeedge with one O(5)MgRh3 trigonal pyramid.
MgCu2(RhO2)4 crystallizes in the triclinic P1 space group. Mg(1) is bonded in a 2-coordinate geometry to one O(1), one O(3), one O(5), and one O(8) atom. The Mg(1)-O(1) bond length is 1.91 Å. The Mg(1)-O(3) bond length is 2.40 Å. The Mg(1)-O(5) bond length is 1.91 Å. The Mg(1)-O(8) bond length is 2.39 Å. There are four inequivalent Rh sites. In the first Rh site, Rh(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(6), and one O(8) atom to form distorted RhO6 octahedra that share corners with three equivalent Cu(1)O4 tetrahedra, edges with two equivalent Rh(2)O6 octahedra, edges with two equivalent Rh(3)O6 octahedra, and edges with two equivalent Rh(4)O6 octahedra. The Rh(1)-O(1) bond length is 2.13 Å. The Rh(1)-O(2) bond length is 2.07 Å. The Rh(1)-O(3) bond length is 2.13 Å. The Rh(1)-O(4) bond length is 2.07 Å. The Rh(1)-O(6) bond length is 2.06 Å. The Rh(1)-O(8) bond length is 2.13 Å. In the second Rh site, Rh(2) is bonded to one O(2), one O(3), one O(4), one O(5), one O(7), and one O(8) atom to form distorted RhO6 octahedra that share corners with three equivalent Cu(1)O4 tetrahedra, edges with two equivalent Rh(1)O6 octahedra, edges with two equivalent Rh(3)O6 octahedra, and edges with two equivalent Rh(4)O6 octahedra. The Rh(2)-O(2) bond length is 2.07 Å. The Rh(2)-O(3) bond length is 2.13 Å. The Rh(2)-O(4) bond length is 2.07 Å. The Rh(2)-O(5) bond length is 2.13 Å. The Rh(2)-O(7) bond length is 2.06 Å. The Rh(2)-O(8) bond length is 2.13 Å. In the third Rh site, Rh(3) is bonded to one O(1), one O(2), one O(5), one O(6), one O(7), and one O(8) atom to form RhO6 octahedra that share corners with three equivalent Cu(1)O4 tetrahedra, edges with two equivalent Rh(1)O6 octahedra, edges with two equivalent Rh(2)O6 octahedra, and edges with two equivalent Rh(4)O6 octahedra. The Rh(3)-O(1) bond length is 2.06 Å. The Rh(3)-O(2) bond length is 2.13 Å. The Rh(3)-O(5) bond length is 2.06 Å. The Rh(3)-O(6) bond length is 2.10 Å. The Rh(3)-O(7) bond length is 2.10 Å. The Rh(3)-O(8) bond length is 2.15 Å. In the fourth Rh site, Rh(4) is bonded to one O(1), one O(3), one O(4), one O(5), one O(6), and one O(7) atom to form RhO6 octahedra that share corners with three equivalent Cu(1)O4 tetrahedra, edges with two equivalent Rh(1)O6 octahedra, edges with two equivalent Rh(2)O6 octahedra, and edges with two equivalent Rh(3)O6 octahedra. The Rh(4)-O(1) bond length is 2.06 Å. The Rh(4)-O(3) bond length is 2.15 Å. The Rh(4)-O(4) bond length is 2.13 Å. The Rh(4)-O(5) bond length is 2.06 Å. The Rh(4)-O(6) bond length is 2.10 Å. The Rh(4)-O(7) bond length is 2.10 Å. There are two inequivalent Cu sites. In the first Cu site, Cu(1) is bonded to one O(3), one O(6), one O(7), and one O(8) atom to form CuO4 tetrahedra that share corners with three equivalent Rh(1)O6 octahedra, corners with three equivalent Rh(2)O6 octahedra, corners with three equivalent Rh(3)O6 octahedra, and corners with three equivalent Rh(4)O6 octahedra. The corner-sharing octahedral tilt angles range from 57-63°. The Cu(1)-O(3) bond length is 2.13 Å. The Cu(1)-O(6) bond length is 2.16 Å. The Cu(1)-O(7) bond length is 2.17 Å. The Cu(1)-O(8) bond length is 2.13 Å. In the second Cu site, Cu(2) is bonded in a distorted linear geometry to one O(2) and one O(4) atom. The Cu(2)-O(2) bond length is 1.81 Å. The Cu(2)-O(4) bond length is 1.81 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Mg(1), one Rh(1), one Rh(3), and one Rh(4) atom to form distorted OMgRh3 trigonal pyramids that share  a cornercorner with one O(8)MgCuRh3 trigonal bipyramid,  a cornercorner with one O(5)MgRh3 trigonal pyramid, corners with two equivalent O(7)CuRh3 trigonal pyramids,  an edgeedge with one O(8)MgCuRh3 trigonal bipyramid,  an edgeedge with one O(2)CuRh3 trigonal pyramid,  an edgeedge with one O(4)CuRh3 trigonal pyramid, and  an edgeedge with one O(5)MgRh3 trigonal pyramid. In the second O site, O(2) is bonded to one Rh(1), one Rh(2), one Rh(3), and one Cu(2) atom to form OCuRh3 trigonal pyramids that share corners with three equivalent O(8)MgCuRh3 trigonal bipyramids,  a cornercorner with one O(4)CuRh3 trigonal pyramid, corners with two equivalent O(7)CuRh3 trigonal pyramids,  an edgeedge with one O(4)CuRh3 trigonal pyramid,  an edgeedge with one O(1)MgRh3 trigonal pyramid, and  an edgeedge with one O(5)MgRh3 trigonal pyramid. In the third O site, O(3) is bonded in a 5-coordinate geometry to one Mg(1), one Rh(1), one Rh(2), one Rh(4), and one Cu(1) atom. In the fourth O site, O(4) is bonded to one Rh(1), one Rh(2), one Rh(4), and one Cu(2) atom to form OCuRh3 trigonal pyramids that share corners with two equivalent O(8)MgCuRh3 trigonal bipyramids,  a cornercorner with one O(2)CuRh3 trigonal pyramid, corners with two equivalent O(7)CuRh3 trigonal pyramids,  an edgeedge with one O(2)CuRh3 trigonal pyramid,  an edgeedge with one O(1)MgRh3 trigonal pyramid, and  an edgeedge with one O(5)MgRh3 trigonal pyramid. In the fifth O site, O(5) is bonded to one Mg(1), one Rh(2), one Rh(3), and one Rh(4) atom to form distorted OMgRh3 trigonal pyramids that share  a cornercorner with one O(8)MgCuRh3 trigonal bipyramid,  a cornercorner with one O(1)MgRh3 trigonal pyramid, corners with three equivalent O(7)CuRh3 trigonal pyramids,  an edgeedge with one O(8)MgCuRh3 trigonal bipyramid,  an edgeedge with one O(2)CuRh3 trigonal pyramid,  an edgeedge with one O(4)CuRh3 trigonal pyramid, and  an edgeedge with one O(1)MgRh3 trigonal pyramid. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Rh(1), one Rh(3), one Rh(4), and one Cu(1) atom. In the seventh O site, O(7) is bonded to one Rh(2), one Rh(3), one Rh(4), and one Cu(1) atom to form distorted OCuRh3 trigonal pyramids that share  a cornercorner with one O(8)MgCuRh3 trigonal bipyramid, corners with two equivalent O(2)CuRh3 trigonal pyramids, corners with two equivalent O(4)CuRh3 trigonal pyramids, corners with two equivalent O(1)MgRh3 trigonal pyramids, corners with three equivalent O(5)MgRh3 trigonal pyramids, and  an edgeedge with one O(8)MgCuRh3 trigonal bipyramid. In the eighth O site, O(8) is bonded to one Mg(1), one Rh(1), one Rh(2), one Rh(3), and one Cu(1) atom to form distorted OMgCuRh3 trigonal bipyramids that share  a cornercorner with one O(7)CuRh3 trigonal pyramid,  a cornercorner with one O(1)MgRh3 trigonal pyramid,  a cornercorner with one O(5)MgRh3 trigonal pyramid, corners with two equivalent O(4)CuRh3 trigonal pyramids, corners with three equivalent O(2)CuRh3 trigonal pyramids,  an edgeedge with one O(7)CuRh3 trigonal pyramid,  an edgeedge with one O(1)MgRh3 trigonal pyramid, and  an edgeedge with one O(5)MgRh3 trigonal pyramid.