Mg7SiN6 crystallizes in the orthorhombic Ibam space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent N(1) and two equivalent N(2) atoms to form MgN4 tetrahedra that share corners with two equivalent Si(1)N4 tetrahedra and  an edgeedge with one Mg(1)N4 tetrahedra. In the second Mg site, Mg(2) is bonded in a 4-coordinate geometry to two equivalent N(1) and two equivalent N(2) atoms. In the third Mg site, Mg(3) is bonded in a 4-coordinate geometry to four equivalent N(1) atoms. Si(1) is bonded to four equivalent N(1) atoms to form SiN4 tetrahedra that share corners with four equivalent Mg(1)N4 tetrahedra. There are two inequivalent N sites. In the first N site, N(1) is bonded in a 5-coordinate geometry to one Mg(1), one Mg(3), two equivalent Mg(2), and one Si(1) atom. In the second N site, N(2) is bonded in a 6-coordinate geometry to two equivalent Mg(1) and four equivalent Mg(2) atoms.
Mg7SiN6 crystallizes in the orthorhombic Ibam space group. There are three inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent N(1) and two equivalent N(2) atoms to form MgN4 tetrahedra that share corners with two equivalent Si(1)N4 tetrahedra and  an edgeedge with one Mg(1)N4 tetrahedra. Both Mg(1)-N(1) bond lengths are 2.14 Å. There is one shorter (2.09 Å) and one longer (2.24 Å) Mg(1)-N(2) bond length. In the second Mg site, Mg(2) is bonded in a 4-coordinate geometry to two equivalent N(1) and two equivalent N(2) atoms. There is one shorter (2.12 Å) and one longer (2.16 Å) Mg(2)-N(1) bond length. There is one shorter (2.15 Å) and one longer (2.23 Å) Mg(2)-N(2) bond length. In the third Mg site, Mg(3) is bonded in a 4-coordinate geometry to four equivalent N(1) atoms. All Mg(3)-N(1) bond lengths are 2.19 Å. Si(1) is bonded to four equivalent N(1) atoms to form SiN4 tetrahedra that share corners with four equivalent Mg(1)N4 tetrahedra. All Si(1)-N(1) bond lengths are 1.76 Å. There are two inequivalent N sites. In the first N site, N(1) is bonded in a 5-coordinate geometry to one Mg(1), one Mg(3), two equivalent Mg(2), and one Si(1) atom. In the second N site, N(2) is bonded in a 6-coordinate geometry to two equivalent Mg(1) and four equivalent Mg(2) atoms.