Mg3MoN4 crystallizes in the monoclinic C2/m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one N(1), one N(3), and three equivalent N(2) atoms to form MgN5 trigonal bipyramids that share corners with three equivalent Mo(1)N4 tetrahedra, corners with two equivalent Mg(2)N5 trigonal bipyramids, corners with four equivalent Mg(1)N5 trigonal bipyramids,  an edgeedge with one Mo(1)N4 tetrahedra, edges with two equivalent Mg(1)N5 trigonal bipyramids, and edges with two equivalent Mg(2)N5 trigonal bipyramids. In the second Mg site, Mg(2) is bonded to one N(3), two equivalent N(1), and two equivalent N(2) atoms to form MgN5 trigonal bipyramids that share corners with three equivalent Mo(1)N4 tetrahedra, corners with four equivalent Mg(1)N5 trigonal bipyramids,  an edgeedge with one Mo(1)N4 tetrahedra,  an edgeedge with one Mg(2)N5 trigonal bipyramid, and edges with four equivalent Mg(1)N5 trigonal bipyramids. Mo(1) is bonded to one N(1), one N(3), and two equivalent N(2) atoms to form distorted MoN4 tetrahedra that share corners with three equivalent Mg(2)N5 trigonal bipyramids, corners with six equivalent Mg(1)N5 trigonal bipyramids,  an edgeedge with one Mg(2)N5 trigonal bipyramid, and edges with two equivalent Mg(1)N5 trigonal bipyramids. There are three inequivalent N sites. In the first N site, N(1) is bonded to two equivalent Mg(1), two equivalent Mg(2), and one Mo(1) atom to form NMg4Mo trigonal bipyramids that share corners with four equivalent N(2)Mg4Mo trigonal bipyramids, corners with three equivalent N(3)Mg3Mo trigonal pyramids,  an edgeedge with one N(1)Mg4Mo trigonal bipyramid, edges with four equivalent N(2)Mg4Mo trigonal bipyramids, and  an edgeedge with one N(3)Mg3Mo trigonal pyramid. In the second N site, N(2) is bonded to one Mg(2), three equivalent Mg(1), and one Mo(1) atom to form NMg4Mo trigonal bipyramids that share corners with two equivalent N(1)Mg4Mo trigonal bipyramids, corners with four equivalent N(2)Mg4Mo trigonal bipyramids, corners with three equivalent N(3)Mg3Mo trigonal pyramids, edges with two equivalent N(1)Mg4Mo trigonal bipyramids, edges with two equivalent N(2)Mg4Mo trigonal bipyramids, and  an edgeedge with one N(3)Mg3Mo trigonal pyramid. In the third N site, N(3) is bonded to one Mg(2), two equivalent Mg(1), and one Mo(1) atom to form a mixture of corner and edge-sharing NMg3Mo trigonal pyramids.
Mg3MoN4 crystallizes in the monoclinic C2/m space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one N(1), one N(3), and three equivalent N(2) atoms to form MgN5 trigonal bipyramids that share corners with three equivalent Mo(1)N4 tetrahedra, corners with two equivalent Mg(2)N5 trigonal bipyramids, corners with four equivalent Mg(1)N5 trigonal bipyramids,  an edgeedge with one Mo(1)N4 tetrahedra, edges with two equivalent Mg(1)N5 trigonal bipyramids, and edges with two equivalent Mg(2)N5 trigonal bipyramids. The Mg(1)-N(1) bond length is 2.12 Å. The Mg(1)-N(3) bond length is 2.07 Å. There are a spread of Mg(1)-N(2) bond distances ranging from 2.12-2.41 Å. In the second Mg site, Mg(2) is bonded to one N(3), two equivalent N(1), and two equivalent N(2) atoms to form MgN5 trigonal bipyramids that share corners with three equivalent Mo(1)N4 tetrahedra, corners with four equivalent Mg(1)N5 trigonal bipyramids,  an edgeedge with one Mo(1)N4 tetrahedra,  an edgeedge with one Mg(2)N5 trigonal bipyramid, and edges with four equivalent Mg(1)N5 trigonal bipyramids. The Mg(2)-N(3) bond length is 2.24 Å. There is one shorter (2.18 Å) and one longer (2.19 Å) Mg(2)-N(1) bond length. Both Mg(2)-N(2) bond lengths are 2.16 Å. Mo(1) is bonded to one N(1), one N(3), and two equivalent N(2) atoms to form distorted MoN4 tetrahedra that share corners with three equivalent Mg(2)N5 trigonal bipyramids, corners with six equivalent Mg(1)N5 trigonal bipyramids,  an edgeedge with one Mg(2)N5 trigonal bipyramid, and edges with two equivalent Mg(1)N5 trigonal bipyramids. The Mo(1)-N(1) bond length is 1.91 Å. The Mo(1)-N(3) bond length is 1.86 Å. Both Mo(1)-N(2) bond lengths are 1.90 Å. There are three inequivalent N sites. In the first N site, N(1) is bonded to two equivalent Mg(1), two equivalent Mg(2), and one Mo(1) atom to form NMg4Mo trigonal bipyramids that share corners with four equivalent N(2)Mg4Mo trigonal bipyramids, corners with three equivalent N(3)Mg3Mo trigonal pyramids,  an edgeedge with one N(1)Mg4Mo trigonal bipyramid, edges with four equivalent N(2)Mg4Mo trigonal bipyramids, and  an edgeedge with one N(3)Mg3Mo trigonal pyramid. In the second N site, N(2) is bonded to one Mg(2), three equivalent Mg(1), and one Mo(1) atom to form NMg4Mo trigonal bipyramids that share corners with two equivalent N(1)Mg4Mo trigonal bipyramids, corners with four equivalent N(2)Mg4Mo trigonal bipyramids, corners with three equivalent N(3)Mg3Mo trigonal pyramids, edges with two equivalent N(1)Mg4Mo trigonal bipyramids, edges with two equivalent N(2)Mg4Mo trigonal bipyramids, and  an edgeedge with one N(3)Mg3Mo trigonal pyramid. In the third N site, N(3) is bonded to one Mg(2), two equivalent Mg(1), and one Mo(1) atom to form a mixture of corner and edge-sharing NMg3Mo trigonal pyramids.