MgS2O7 crystallizes in the triclinic P-1 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(7) atoms to form MgO6 octahedra that share corners with two equivalent S(2)O4 tetrahedra and corners with four equivalent S(1)O4 tetrahedra. In the second Mg site, Mg(2) is bonded to two equivalent O(3), two equivalent O(5), and two equivalent O(6) atoms to form MgO6 octahedra that share corners with two equivalent S(1)O4 tetrahedra and corners with four equivalent S(2)O4 tetrahedra. There are two inequivalent S sites. In the first S site, S(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SO4 tetrahedra that share  a cornercorner with one Mg(2)O6 octahedra, corners with two equivalent Mg(1)O6 octahedra, and  a cornercorner with one S(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 28-47°. In the second S site, S(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form SO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra, corners with two equivalent Mg(2)O6 octahedra, and  a cornercorner with one S(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 36-44°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Mg(1) and one S(1) atom. In the second O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Mg(1) and one S(1) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Mg(2) and one S(1) atom. In the fourth O site, O(4) is bonded in a bent 120 degrees geometry to one S(1) and one S(2) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Mg(2) and one S(2) atom. In the sixth O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Mg(2) and one S(2) atom. In the seventh O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Mg(1) and one S(2) atom.
MgS2O7 crystallizes in the triclinic P-1 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(7) atoms to form MgO6 octahedra that share corners with two equivalent S(2)O4 tetrahedra and corners with four equivalent S(1)O4 tetrahedra. Both Mg(1)-O(1) bond lengths are 2.05 Å. Both Mg(1)-O(2) bond lengths are 2.06 Å. Both Mg(1)-O(7) bond lengths are 2.05 Å. In the second Mg site, Mg(2) is bonded to two equivalent O(3), two equivalent O(5), and two equivalent O(6) atoms to form MgO6 octahedra that share corners with two equivalent S(1)O4 tetrahedra and corners with four equivalent S(2)O4 tetrahedra. Both Mg(2)-O(3) bond lengths are 2.04 Å. Both Mg(2)-O(5) bond lengths are 2.04 Å. Both Mg(2)-O(6) bond lengths are 2.06 Å. There are two inequivalent S sites. In the first S site, S(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form SO4 tetrahedra that share  a cornercorner with one Mg(2)O6 octahedra, corners with two equivalent Mg(1)O6 octahedra, and  a cornercorner with one S(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 28-47°. The S(1)-O(1) bond length is 1.44 Å. The S(1)-O(2) bond length is 1.44 Å. The S(1)-O(3) bond length is 1.43 Å. The S(1)-O(4) bond length is 1.63 Å. In the second S site, S(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form SO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra, corners with two equivalent Mg(2)O6 octahedra, and  a cornercorner with one S(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 36-44°. The S(2)-O(4) bond length is 1.64 Å. The S(2)-O(5) bond length is 1.43 Å. The S(2)-O(6) bond length is 1.44 Å. The S(2)-O(7) bond length is 1.44 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one Mg(1) and one S(1) atom. In the second O site, O(2) is bonded in a distorted bent 120 degrees geometry to one Mg(1) and one S(1) atom. In the third O site, O(3) is bonded in a bent 150 degrees geometry to one Mg(2) and one S(1) atom. In the fourth O site, O(4) is bonded in a bent 120 degrees geometry to one S(1) and one S(2) atom. In the fifth O site, O(5) is bonded in a bent 150 degrees geometry to one Mg(2) and one S(2) atom. In the sixth O site, O(6) is bonded in a distorted bent 150 degrees geometry to one Mg(2) and one S(2) atom. In the seventh O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Mg(1) and one S(2) atom.