Fe3SiN4 crystallizes in the orthorhombic Pmn2_1 space group. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one N(2), one N(3), and two equivalent N(1) atoms to form distorted FeN4 tetrahedra that share corners with two equivalent Fe(2)N4 tetrahedra, corners with two equivalent Si(1)N4 tetrahedra, corners with four equivalent Fe(1)N4 tetrahedra,  an edgeedge with one Fe(2)N4 tetrahedra, and  an edgeedge with one Si(1)N4 tetrahedra. In the second Fe site, Fe(2) is bonded to one N(2), one N(3), and two equivalent N(1) atoms to form distorted FeN4 tetrahedra that share corners with four equivalent Fe(1)N4 tetrahedra, corners with four equivalent Si(1)N4 tetrahedra, and edges with two equivalent Fe(1)N4 tetrahedra. Si(1) is bonded to one N(2), one N(3), and two equivalent N(1) atoms to form SiN4 tetrahedra that share corners with four equivalent Fe(1)N4 tetrahedra, corners with four equivalent Fe(2)N4 tetrahedra, and edges with two equivalent Fe(1)N4 tetrahedra. There are three inequivalent N sites. In the first N site, N(1) is bonded to one Fe(2), two equivalent Fe(1), and one Si(1) atom to form a mixture of distorted edge and corner-sharing NFe3Si trigonal pyramids. In the second N site, N(2) is bonded to one Fe(2), two equivalent Fe(1), and one Si(1) atom to form a mixture of distorted edge and corner-sharing NFe3Si trigonal pyramids. In the third N site, N(3) is bonded to one Fe(2), two equivalent Fe(1), and one Si(1) atom to form a mixture of distorted edge and corner-sharing NFe3Si trigonal pyramids.
Fe3SiN4 crystallizes in the orthorhombic Pmn2_1 space group. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one N(2), one N(3), and two equivalent N(1) atoms to form distorted FeN4 tetrahedra that share corners with two equivalent Fe(2)N4 tetrahedra, corners with two equivalent Si(1)N4 tetrahedra, corners with four equivalent Fe(1)N4 tetrahedra,  an edgeedge with one Fe(2)N4 tetrahedra, and  an edgeedge with one Si(1)N4 tetrahedra. The Fe(1)-N(2) bond length is 1.87 Å. The Fe(1)-N(3) bond length is 1.92 Å. There is one shorter (1.82 Å) and one longer (1.94 Å) Fe(1)-N(1) bond length. In the second Fe site, Fe(2) is bonded to one N(2), one N(3), and two equivalent N(1) atoms to form distorted FeN4 tetrahedra that share corners with four equivalent Fe(1)N4 tetrahedra, corners with four equivalent Si(1)N4 tetrahedra, and edges with two equivalent Fe(1)N4 tetrahedra. The Fe(2)-N(2) bond length is 1.89 Å. The Fe(2)-N(3) bond length is 1.86 Å. Both Fe(2)-N(1) bond lengths are 1.88 Å. Si(1) is bonded to one N(2), one N(3), and two equivalent N(1) atoms to form SiN4 tetrahedra that share corners with four equivalent Fe(1)N4 tetrahedra, corners with four equivalent Fe(2)N4 tetrahedra, and edges with two equivalent Fe(1)N4 tetrahedra. The Si(1)-N(2) bond length is 1.72 Å. The Si(1)-N(3) bond length is 1.77 Å. Both Si(1)-N(1) bond lengths are 1.74 Å. There are three inequivalent N sites. In the first N site, N(1) is bonded to one Fe(2), two equivalent Fe(1), and one Si(1) atom to form a mixture of distorted edge and corner-sharing NFe3Si trigonal pyramids. In the second N site, N(2) is bonded to one Fe(2), two equivalent Fe(1), and one Si(1) atom to form a mixture of distorted edge and corner-sharing NFe3Si trigonal pyramids. In the third N site, N(3) is bonded to one Fe(2), two equivalent Fe(1), and one Si(1) atom to form a mixture of distorted edge and corner-sharing NFe3Si trigonal pyramids.