FeP4 is Sylvanite-derived structured and crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one P(1), one P(3), one P(4), one P(6), and two equivalent P(2) atoms to form FeP6 octahedra that share corners with two equivalent Fe(1)P6 octahedra, corners with two equivalent P(4)Fe2P2 tetrahedra, corners with three equivalent P(1)FeP3 tetrahedra, corners with four equivalent P(5)FeP3 tetrahedra, and  an edgeedge with one Fe(2)P6 octahedra. The corner-sharing octahedral tilt angles are 54°. In the second Fe site, Fe(2) is bonded to two equivalent P(3), two equivalent P(4), and two equivalent P(5) atoms to form FeP6 octahedra that share corners with two equivalent P(4)Fe2P2 tetrahedra, corners with four equivalent P(1)FeP3 tetrahedra, and edges with two equivalent Fe(1)P6 octahedra. There are six inequivalent P sites. In the first P site, P(1) is bonded to one Fe(1), one P(2), one P(4), and one P(5) atom to form distorted PFeP3 tetrahedra that share corners with two equivalent Fe(2)P6 octahedra, corners with three equivalent Fe(1)P6 octahedra,  a cornercorner with one P(4)Fe2P2 tetrahedra, and  a cornercorner with one P(5)FeP3 tetrahedra. The corner-sharing octahedral tilt angles range from 62-79°. In the second P site, P(2) is bonded in a 4-coordinate geometry to two equivalent Fe(1), one P(1), and one P(5) atom. In the third P site, P(3) is bonded in a 4-coordinate geometry to one Fe(1), one Fe(2), one P(4), and one P(6) atom. In the fourth P site, P(4) is bonded to one Fe(1), one Fe(2), one P(1), and one P(3) atom to form distorted PFe2P2 tetrahedra that share  a cornercorner with one Fe(2)P6 octahedra, corners with two equivalent Fe(1)P6 octahedra,  a cornercorner with one P(4)Fe2P2 tetrahedra,  a cornercorner with one P(1)FeP3 tetrahedra, and corners with three equivalent P(5)FeP3 tetrahedra. The corner-sharing octahedral tilt angles range from 64-70°. In the fifth P site, P(5) is bonded to one Fe(2), one P(1), one P(2), and one P(6) atom to form distorted PFeP3 tetrahedra that share corners with four equivalent Fe(1)P6 octahedra,  a cornercorner with one P(1)FeP3 tetrahedra,  a cornercorner with one P(5)FeP3 tetrahedra, and corners with three equivalent P(4)Fe2P2 tetrahedra. The corner-sharing octahedral tilt angles range from 45-79°. In the sixth P site, P(6) is bonded in a distorted single-bond geometry to one Fe(1), one P(3), one P(5), and one P(6) atom.
FeP4 is Sylvanite-derived structured and crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to one P(1), one P(3), one P(4), one P(6), and two equivalent P(2) atoms to form FeP6 octahedra that share corners with two equivalent Fe(1)P6 octahedra, corners with two equivalent P(4)Fe2P2 tetrahedra, corners with three equivalent P(1)FeP3 tetrahedra, corners with four equivalent P(5)FeP3 tetrahedra, and  an edgeedge with one Fe(2)P6 octahedra. The corner-sharing octahedral tilt angles are 54°. The Fe(1)-P(1) bond length is 2.21 Å. The Fe(1)-P(3) bond length is 2.28 Å. The Fe(1)-P(4) bond length is 2.21 Å. The Fe(1)-P(6) bond length is 2.16 Å. There is one shorter (2.31 Å) and one longer (2.33 Å) Fe(1)-P(2) bond length. In the second Fe site, Fe(2) is bonded to two equivalent P(3), two equivalent P(4), and two equivalent P(5) atoms to form FeP6 octahedra that share corners with two equivalent P(4)Fe2P2 tetrahedra, corners with four equivalent P(1)FeP3 tetrahedra, and edges with two equivalent Fe(1)P6 octahedra. Both Fe(2)-P(3) bond lengths are 2.24 Å. Both Fe(2)-P(4) bond lengths are 2.25 Å. Both Fe(2)-P(5) bond lengths are 2.25 Å. There are six inequivalent P sites. In the first P site, P(1) is bonded to one Fe(1), one P(2), one P(4), and one P(5) atom to form distorted PFeP3 tetrahedra that share corners with two equivalent Fe(2)P6 octahedra, corners with three equivalent Fe(1)P6 octahedra,  a cornercorner with one P(4)Fe2P2 tetrahedra, and  a cornercorner with one P(5)FeP3 tetrahedra. The corner-sharing octahedral tilt angles range from 62-79°. The P(1)-P(2) bond length is 2.24 Å. The P(1)-P(4) bond length is 2.16 Å. The P(1)-P(5) bond length is 2.28 Å. In the second P site, P(2) is bonded in a 4-coordinate geometry to two equivalent Fe(1), one P(1), and one P(5) atom. The P(2)-P(5) bond length is 2.21 Å. In the third P site, P(3) is bonded in a 4-coordinate geometry to one Fe(1), one Fe(2), one P(4), and one P(6) atom. The P(3)-P(4) bond length is 2.21 Å. The P(3)-P(6) bond length is 2.20 Å. In the fourth P site, P(4) is bonded to one Fe(1), one Fe(2), one P(1), and one P(3) atom to form distorted PFe2P2 tetrahedra that share  a cornercorner with one Fe(2)P6 octahedra, corners with two equivalent Fe(1)P6 octahedra,  a cornercorner with one P(4)Fe2P2 tetrahedra,  a cornercorner with one P(1)FeP3 tetrahedra, and corners with three equivalent P(5)FeP3 tetrahedra. The corner-sharing octahedral tilt angles range from 64-70°. In the fifth P site, P(5) is bonded to one Fe(2), one P(1), one P(2), and one P(6) atom to form distorted PFeP3 tetrahedra that share corners with four equivalent Fe(1)P6 octahedra,  a cornercorner with one P(1)FeP3 tetrahedra,  a cornercorner with one P(5)FeP3 tetrahedra, and corners with three equivalent P(4)Fe2P2 tetrahedra. The corner-sharing octahedral tilt angles range from 45-79°. The P(5)-P(6) bond length is 2.24 Å. In the sixth P site, P(6) is bonded in a distorted single-bond geometry to one Fe(1), one P(3), one P(5), and one P(6) atom. The P(6)-P(6) bond length is 2.29 Å.