LaFe9Si4 crystallizes in the tetragonal I4/mcm space group. La(1) is bonded in a 24-coordinate geometry to eight equivalent Fe(1), eight equivalent Fe(2), and eight equivalent Si(1) atoms. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent La(1), one Fe(3), two equivalent Fe(2), three equivalent Fe(1), and four equivalent Si(1) atoms to form distorted FeLa2Fe6Si4 cuboctahedra that share  a cornercorner with one Fe(3)Fe8Si4 cuboctahedra, corners with eleven equivalent Fe(1)La2Fe6Si4 cuboctahedra, faces with two equivalent Fe(3)Fe8Si4 cuboctahedra, and faces with seven equivalent Fe(1)La2Fe6Si4 cuboctahedra. In the second Fe site, Fe(2) is bonded in a 12-coordinate geometry to two equivalent La(1), one Fe(3), two equivalent Fe(1), three equivalent Fe(2), and four equivalent Si(1) atoms. In the third Fe site, Fe(3) is bonded to four equivalent Fe(1), four equivalent Fe(2), and four equivalent Si(1) atoms to form a mixture of face and corner-sharing FeFe8Si4 cuboctahedra. Si(1) is bonded in a 12-coordinate geometry to two equivalent La(1), one Fe(3), four equivalent Fe(1), four equivalent Fe(2), and one Si(1) atom.
LaFe9Si4 crystallizes in the tetragonal I4/mcm space group. La(1) is bonded in a 24-coordinate geometry to eight equivalent Fe(1), eight equivalent Fe(2), and eight equivalent Si(1) atoms. All La(1)-Fe(1) bond lengths are 3.34 Å. All La(1)-Fe(2) bond lengths are 3.26 Å. All La(1)-Si(1) bond lengths are 3.28 Å. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent La(1), one Fe(3), two equivalent Fe(2), three equivalent Fe(1), and four equivalent Si(1) atoms to form distorted FeLa2Fe6Si4 cuboctahedra that share  a cornercorner with one Fe(3)Fe8Si4 cuboctahedra, corners with eleven equivalent Fe(1)La2Fe6Si4 cuboctahedra, faces with two equivalent Fe(3)Fe8Si4 cuboctahedra, and faces with seven equivalent Fe(1)La2Fe6Si4 cuboctahedra. The Fe(1)-Fe(3) bond length is 2.42 Å. Both Fe(1)-Fe(2) bond lengths are 2.56 Å. There are two shorter (2.36 Å) and one longer (2.63 Å) Fe(1)-Fe(1) bond length. There are two shorter (2.49 Å) and two longer (2.54 Å) Fe(1)-Si(1) bond lengths. In the second Fe site, Fe(2) is bonded in a 12-coordinate geometry to two equivalent La(1), one Fe(3), two equivalent Fe(1), three equivalent Fe(2), and four equivalent Si(1) atoms. The Fe(2)-Fe(3) bond length is 2.48 Å. There are two shorter (2.48 Å) and one longer (2.67 Å) Fe(2)-Fe(2) bond length. There are a spread of Fe(2)-Si(1) bond distances ranging from 2.39-2.48 Å. In the third Fe site, Fe(3) is bonded to four equivalent Fe(1), four equivalent Fe(2), and four equivalent Si(1) atoms to form a mixture of face and corner-sharing FeFe8Si4 cuboctahedra. All Fe(3)-Si(1) bond lengths are 2.41 Å. Si(1) is bonded in a 12-coordinate geometry to two equivalent La(1), one Fe(3), four equivalent Fe(1), four equivalent Fe(2), and one Si(1) atom. The Si(1)-Si(1) bond length is 2.78 Å.