Li4Sr3(SiN3)2 crystallizes in the monoclinic C2/m space group. Li(1) is bonded to one N(2) and three equivalent N(1) atoms to form distorted LiN4 tetrahedra that share corners with three equivalent Li(1)N4 tetrahedra, corners with three equivalent Si(1)N4 tetrahedra,  an edgeedge with one Si(1)N4 tetrahedra, and edges with two equivalent Li(1)N4 tetrahedra. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 6-coordinate geometry to two equivalent N(2) and four equivalent N(1) atoms. In the second Sr site, Sr(2) is bonded in a 4-coordinate geometry to four equivalent N(1) atoms. Si(1) is bonded to two equivalent N(1) and two equivalent N(2) atoms to form SiN4 tetrahedra that share corners with six equivalent Li(1)N4 tetrahedra,  an edgeedge with one Si(1)N4 tetrahedra, and edges with two equivalent Li(1)N4 tetrahedra. There are two inequivalent N sites. In the first N site, N(1) is bonded in a 7-coordinate geometry to three equivalent Li(1), one Sr(2), two equivalent Sr(1), and one Si(1) atom. In the second N site, N(2) is bonded in a 4-coordinate geometry to two equivalent Li(1), two equivalent Sr(1), and two equivalent Si(1) atoms.
Li4Sr3(SiN3)2 crystallizes in the monoclinic C2/m space group. Li(1) is bonded to one N(2) and three equivalent N(1) atoms to form distorted LiN4 tetrahedra that share corners with three equivalent Li(1)N4 tetrahedra, corners with three equivalent Si(1)N4 tetrahedra,  an edgeedge with one Si(1)N4 tetrahedra, and edges with two equivalent Li(1)N4 tetrahedra. The Li(1)-N(2) bond length is 2.37 Å. There are a spread of Li(1)-N(1) bond distances ranging from 2.04-2.17 Å. There are two inequivalent Sr sites. In the first Sr site, Sr(1) is bonded in a 6-coordinate geometry to two equivalent N(2) and four equivalent N(1) atoms. Both Sr(1)-N(2) bond lengths are 2.82 Å. There are two shorter (2.64 Å) and two longer (2.71 Å) Sr(1)-N(1) bond lengths. In the second Sr site, Sr(2) is bonded in a 4-coordinate geometry to four equivalent N(1) atoms. All Sr(2)-N(1) bond lengths are 2.68 Å. Si(1) is bonded to two equivalent N(1) and two equivalent N(2) atoms to form SiN4 tetrahedra that share corners with six equivalent Li(1)N4 tetrahedra,  an edgeedge with one Si(1)N4 tetrahedra, and edges with two equivalent Li(1)N4 tetrahedra. Both Si(1)-N(1) bond lengths are 1.74 Å. There is one shorter (1.83 Å) and one longer (1.88 Å) Si(1)-N(2) bond length. There are two inequivalent N sites. In the first N site, N(1) is bonded in a 7-coordinate geometry to three equivalent Li(1), one Sr(2), two equivalent Sr(1), and one Si(1) atom. In the second N site, N(2) is bonded in a 4-coordinate geometry to two equivalent Li(1), two equivalent Sr(1), and two equivalent Si(1) atoms.