MgFe2Si2SbO9 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(1), one O(2), one O(3), one O(7), and one O(8) atom to form distorted MgO5 trigonal bipyramids that share corners with three equivalent Fe(1)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra,  an edgeedge with one Si(2)O4 tetrahedra, and  a faceface with one Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 42-50°. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form distorted FeO6 octahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, corners with three equivalent Mg(1)O5 trigonal bipyramids, and edges with three equivalent Fe(2)O6 octahedra. In the second Fe site, Fe(2) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form distorted FeO6 octahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, edges with three equivalent Fe(1)O6 octahedra, and  a faceface with one Mg(1)O5 trigonal bipyramid. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(4), one O(7), one O(8), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one Fe(2)O6 octahedra, corners with three equivalent Si(2)O4 tetrahedra, and corners with two equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 53-58°. In the second Si site, Si(2) is bonded to one O(5), one O(7), one O(8), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one Fe(2)O6 octahedra, corners with three equivalent Si(1)O4 tetrahedra, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 56-68°. Sb(1) is bonded in a trigonal non-coplanar geometry to one O(1), one O(2), and one O(3) atom. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Mg(1), one Fe(1), one Fe(2), and one Sb(1) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Mg(1), one Fe(1), one Fe(2), and one Sb(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Mg(1), one Fe(1), one Fe(2), and one Sb(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(2), and one Si(1) atom. In the fifth O site, O(5) is bonded in a distorted trigonal non-coplanar geometry to one Fe(1), one Fe(2), and one Si(2) atom. In the sixth O site, O(6) is bonded in a water-like geometry to one Fe(1) and one Fe(2) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Mg(1), one Si(1), and one Si(2) atom. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Mg(1), one Si(1), and one Si(2) atom. In the ninth O site, O(9) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom.
MgFe2Si2SbO9 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(1), one O(2), one O(3), one O(7), and one O(8) atom to form distorted MgO5 trigonal bipyramids that share corners with three equivalent Fe(1)O6 octahedra, corners with two equivalent Si(1)O4 tetrahedra,  an edgeedge with one Si(2)O4 tetrahedra, and  a faceface with one Fe(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 42-50°. The Mg(1)-O(1) bond length is 2.04 Å. The Mg(1)-O(2) bond length is 2.01 Å. The Mg(1)-O(3) bond length is 2.05 Å. The Mg(1)-O(7) bond length is 2.39 Å. The Mg(1)-O(8) bond length is 2.25 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form distorted FeO6 octahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, corners with three equivalent Mg(1)O5 trigonal bipyramids, and edges with three equivalent Fe(2)O6 octahedra. The Fe(1)-O(1) bond length is 2.39 Å. The Fe(1)-O(2) bond length is 2.13 Å. The Fe(1)-O(3) bond length is 2.17 Å. The Fe(1)-O(4) bond length is 2.09 Å. The Fe(1)-O(5) bond length is 2.04 Å. The Fe(1)-O(6) bond length is 1.82 Å. In the second Fe site, Fe(2) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form distorted FeO6 octahedra that share  a cornercorner with one Si(1)O4 tetrahedra,  a cornercorner with one Si(2)O4 tetrahedra, edges with three equivalent Fe(1)O6 octahedra, and  a faceface with one Mg(1)O5 trigonal bipyramid. The Fe(2)-O(1) bond length is 2.26 Å. The Fe(2)-O(2) bond length is 2.30 Å. The Fe(2)-O(3) bond length is 2.33 Å. The Fe(2)-O(4) bond length is 2.05 Å. The Fe(2)-O(5) bond length is 2.10 Å. The Fe(2)-O(6) bond length is 1.95 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(4), one O(7), one O(8), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one Fe(2)O6 octahedra, corners with three equivalent Si(2)O4 tetrahedra, and corners with two equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 53-58°. The Si(1)-O(4) bond length is 1.59 Å. The Si(1)-O(7) bond length is 1.70 Å. The Si(1)-O(8) bond length is 1.72 Å. The Si(1)-O(9) bond length is 1.65 Å. In the second Si site, Si(2) is bonded to one O(5), one O(7), one O(8), and one O(9) atom to form SiO4 tetrahedra that share  a cornercorner with one Fe(1)O6 octahedra,  a cornercorner with one Fe(2)O6 octahedra, corners with three equivalent Si(1)O4 tetrahedra, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 56-68°. The Si(2)-O(5) bond length is 1.58 Å. The Si(2)-O(7) bond length is 1.70 Å. The Si(2)-O(8) bond length is 1.71 Å. The Si(2)-O(9) bond length is 1.66 Å. Sb(1) is bonded in a trigonal non-coplanar geometry to one O(1), one O(2), and one O(3) atom. The Sb(1)-O(1) bond length is 2.00 Å. The Sb(1)-O(2) bond length is 2.02 Å. The Sb(1)-O(3) bond length is 2.00 Å. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a 4-coordinate geometry to one Mg(1), one Fe(1), one Fe(2), and one Sb(1) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Mg(1), one Fe(1), one Fe(2), and one Sb(1) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Mg(1), one Fe(1), one Fe(2), and one Sb(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Fe(1), one Fe(2), and one Si(1) atom. In the fifth O site, O(5) is bonded in a distorted trigonal non-coplanar geometry to one Fe(1), one Fe(2), and one Si(2) atom. In the sixth O site, O(6) is bonded in a water-like geometry to one Fe(1) and one Fe(2) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Mg(1), one Si(1), and one Si(2) atom. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Mg(1), one Si(1), and one Si(2) atom. In the ninth O site, O(9) is bonded in a bent 150 degrees geometry to one Si(1) and one Si(2) atom.