MgFe4(HgO4)2 is Aluminum carbonitride-derived structured and crystallizes in the orthorhombic Imm2 space group. Mg(1) is bonded to two equivalent O(1) and two equivalent O(3) atoms to form distorted MgO4 tetrahedra that share corners with six equivalent Fe(1)O6 octahedra and corners with two equivalent Hg(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 28-56°. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(2), one O(3), two equivalent O(1), and two equivalent O(4) atoms to form FeO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, corners with three equivalent Hg(2)O4 tetrahedra, and edges with two equivalent Fe(1)O6 octahedra. In the second Fe site, Fe(2) is bonded in a 5-coordinate geometry to one O(4), two equivalent O(2), and two equivalent O(3) atoms. There are two inequivalent Hg sites. In the first Hg site, Hg(1) is bonded in a 4-coordinate geometry to two equivalent O(1) and two equivalent O(2) atoms. In the second Hg site, Hg(2) is bonded to two equivalent O(3) and two equivalent O(4) atoms to form HgO4 tetrahedra that share corners with six equivalent Fe(1)O6 octahedra and corners with two equivalent Mg(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 60-68°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Mg(1), two equivalent Fe(1), and one Hg(1) atom. In the second O site, O(2) is bonded to one Fe(1), two equivalent Fe(2), and one Hg(1) atom to form OFe3Hg tetrahedra that share  a cornercorner with one O(2)Fe3Hg tetrahedra, corners with four equivalent O(4)Fe3Hg tetrahedra, corners with five equivalent O(3)MgFe3Hg trigonal bipyramids, and  an edgeedge with one O(2)Fe3Hg tetrahedra. In the third O site, O(3) is bonded to one Mg(1), one Fe(1), two equivalent Fe(2), and one Hg(2) atom to form distorted OMgFe3Hg trigonal bipyramids that share corners with two equivalent O(4)Fe3Hg tetrahedra, corners with five equivalent O(2)Fe3Hg tetrahedra,  a cornercorner with one O(3)MgFe3Hg trigonal bipyramid, edges with two equivalent O(4)Fe3Hg tetrahedra, and  a faceface with one O(3)MgFe3Hg trigonal bipyramid. In the fourth O site, O(4) is bonded to one Fe(2), two equivalent Fe(1), and one Hg(2) atom to form distorted OFe3Hg tetrahedra that share  a cornercorner with one O(4)Fe3Hg tetrahedra, corners with four equivalent O(2)Fe3Hg tetrahedra, corners with two equivalent O(3)MgFe3Hg trigonal bipyramids,  an edgeedge with one O(4)Fe3Hg tetrahedra, and edges with two equivalent O(3)MgFe3Hg trigonal bipyramids.
MgFe4(HgO4)2 is Aluminum carbonitride-derived structured and crystallizes in the orthorhombic Imm2 space group. Mg(1) is bonded to two equivalent O(1) and two equivalent O(3) atoms to form distorted MgO4 tetrahedra that share corners with six equivalent Fe(1)O6 octahedra and corners with two equivalent Hg(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 28-56°. Both Mg(1)-O(1) bond lengths are 2.00 Å. Both Mg(1)-O(3) bond lengths are 2.14 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(2), one O(3), two equivalent O(1), and two equivalent O(4) atoms to form FeO6 octahedra that share corners with three equivalent Mg(1)O4 tetrahedra, corners with three equivalent Hg(2)O4 tetrahedra, and edges with two equivalent Fe(1)O6 octahedra. The Fe(1)-O(2) bond length is 2.07 Å. The Fe(1)-O(3) bond length is 2.14 Å. Both Fe(1)-O(1) bond lengths are 2.09 Å. Both Fe(1)-O(4) bond lengths are 2.12 Å. In the second Fe site, Fe(2) is bonded in a 5-coordinate geometry to one O(4), two equivalent O(2), and two equivalent O(3) atoms. The Fe(2)-O(4) bond length is 2.03 Å. Both Fe(2)-O(2) bond lengths are 2.05 Å. Both Fe(2)-O(3) bond lengths are 2.19 Å. There are two inequivalent Hg sites. In the first Hg site, Hg(1) is bonded in a 4-coordinate geometry to two equivalent O(1) and two equivalent O(2) atoms. Both Hg(1)-O(1) bond lengths are 2.52 Å. Both Hg(1)-O(2) bond lengths are 2.11 Å. In the second Hg site, Hg(2) is bonded to two equivalent O(3) and two equivalent O(4) atoms to form HgO4 tetrahedra that share corners with six equivalent Fe(1)O6 octahedra and corners with two equivalent Mg(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 60-68°. Both Hg(2)-O(3) bond lengths are 2.25 Å. Both Hg(2)-O(4) bond lengths are 2.31 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Mg(1), two equivalent Fe(1), and one Hg(1) atom. In the second O site, O(2) is bonded to one Fe(1), two equivalent Fe(2), and one Hg(1) atom to form OFe3Hg tetrahedra that share  a cornercorner with one O(2)Fe3Hg tetrahedra, corners with four equivalent O(4)Fe3Hg tetrahedra, corners with five equivalent O(3)MgFe3Hg trigonal bipyramids, and  an edgeedge with one O(2)Fe3Hg tetrahedra. In the third O site, O(3) is bonded to one Mg(1), one Fe(1), two equivalent Fe(2), and one Hg(2) atom to form distorted OMgFe3Hg trigonal bipyramids that share corners with two equivalent O(4)Fe3Hg tetrahedra, corners with five equivalent O(2)Fe3Hg tetrahedra,  a cornercorner with one O(3)MgFe3Hg trigonal bipyramid, edges with two equivalent O(4)Fe3Hg tetrahedra, and  a faceface with one O(3)MgFe3Hg trigonal bipyramid. In the fourth O site, O(4) is bonded to one Fe(2), two equivalent Fe(1), and one Hg(2) atom to form distorted OFe3Hg tetrahedra that share  a cornercorner with one O(4)Fe3Hg tetrahedra, corners with four equivalent O(2)Fe3Hg tetrahedra, corners with two equivalent O(3)MgFe3Hg trigonal bipyramids,  an edgeedge with one O(4)Fe3Hg tetrahedra, and edges with two equivalent O(3)MgFe3Hg trigonal bipyramids.