Sr2MgGe2O7 crystallizes in the tetragonal P-42_1m space group. Sr(1) is bonded in a 8-coordinate geometry to one O(1), three equivalent O(3), and four equivalent O(2) atoms. Mg(1) is bonded to four equivalent O(2) atoms to form MgO4 tetrahedra that share corners with four equivalent Ge(1)O4 tetrahedra. Ge(1) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form GeO4 tetrahedra that share  a cornercorner with one Ge(1)O4 tetrahedra and corners with two equivalent Mg(1)O4 tetrahedra. There are three inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Sr(1) and two equivalent Ge(1) atoms to form a mixture of distorted edge and corner-sharing OSr2Ge2 tetrahedra. In the second O site, O(2) is bonded in a 4-coordinate geometry to two equivalent Sr(1), one Mg(1), and one Ge(1) atom. In the third O site, O(3) is bonded to three equivalent Sr(1) and one Ge(1) atom to form distorted OSr3Ge tetrahedra that share corners with two equivalent O(1)Sr2Ge2 tetrahedra, corners with four equivalent O(3)Sr3Ge tetrahedra,  an edgeedge with one O(1)Sr2Ge2 tetrahedra, and  an edgeedge with one O(3)Sr3Ge tetrahedra.
Sr2MgGe2O7 crystallizes in the tetragonal P-42_1m space group. Sr(1) is bonded in a 8-coordinate geometry to one O(1), three equivalent O(3), and four equivalent O(2) atoms. The Sr(1)-O(1) bond length is 2.60 Å. There is one shorter (2.61 Å) and two longer (2.78 Å) Sr(1)-O(3) bond lengths. There are two shorter (2.59 Å) and two longer (2.91 Å) Sr(1)-O(2) bond lengths. Mg(1) is bonded to four equivalent O(2) atoms to form MgO4 tetrahedra that share corners with four equivalent Ge(1)O4 tetrahedra. All Mg(1)-O(2) bond lengths are 1.96 Å. Ge(1) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form GeO4 tetrahedra that share  a cornercorner with one Ge(1)O4 tetrahedra and corners with two equivalent Mg(1)O4 tetrahedra. The Ge(1)-O(1) bond length is 1.82 Å. The Ge(1)-O(3) bond length is 1.74 Å. Both Ge(1)-O(2) bond lengths are 1.77 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Sr(1) and two equivalent Ge(1) atoms to form a mixture of distorted edge and corner-sharing OSr2Ge2 tetrahedra. In the second O site, O(2) is bonded in a 4-coordinate geometry to two equivalent Sr(1), one Mg(1), and one Ge(1) atom. In the third O site, O(3) is bonded to three equivalent Sr(1) and one Ge(1) atom to form distorted OSr3Ge tetrahedra that share corners with two equivalent O(1)Sr2Ge2 tetrahedra, corners with four equivalent O(3)Sr3Ge tetrahedra,  an edgeedge with one O(1)Sr2Ge2 tetrahedra, and  an edgeedge with one O(3)Sr3Ge tetrahedra.