Fe3NiAs4 is Modderite-derived structured and crystallizes in the monoclinic Pm space group. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 6-coordinate geometry to one As(1), one As(2), two equivalent As(3), and two equivalent As(4) atoms. In the second Fe site, Fe(2) is bonded to one As(3), one As(4), two equivalent As(1), and two equivalent As(2) atoms to form distorted edge-sharing FeAs6 octahedra. In the third Fe site, Fe(3) is bonded in a 6-coordinate geometry to one As(3), one As(4), two equivalent As(1), and two equivalent As(2) atoms. Ni(1) is bonded in a 6-coordinate geometry to one As(1), one As(2), two equivalent As(3), and two equivalent As(4) atoms. There are four inequivalent As sites. In the first As site, As(1) is bonded in a 6-coordinate geometry to one Fe(1), two equivalent Fe(2), two equivalent Fe(3), and one Ni(1) atom. In the second As site, As(2) is bonded in a 6-coordinate geometry to one Fe(1), two equivalent Fe(2), two equivalent Fe(3), and one Ni(1) atom. In the third As site, As(3) is bonded in a 6-coordinate geometry to one Fe(2), one Fe(3), two equivalent Fe(1), and two equivalent Ni(1) atoms. In the fourth As site, As(4) is bonded in a 6-coordinate geometry to one Fe(2), one Fe(3), two equivalent Fe(1), and two equivalent Ni(1) atoms.
Fe3NiAs4 is Modderite-derived structured and crystallizes in the monoclinic Pm space group. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 6-coordinate geometry to one As(1), one As(2), two equivalent As(3), and two equivalent As(4) atoms. The Fe(1)-As(1) bond length is 2.29 Å. The Fe(1)-As(2) bond length is 2.50 Å. Both Fe(1)-As(3) bond lengths are 2.41 Å. Both Fe(1)-As(4) bond lengths are 2.36 Å. In the second Fe site, Fe(2) is bonded to one As(3), one As(4), two equivalent As(1), and two equivalent As(2) atoms to form distorted edge-sharing FeAs6 octahedra. The Fe(2)-As(3) bond length is 2.42 Å. The Fe(2)-As(4) bond length is 2.33 Å. Both Fe(2)-As(1) bond lengths are 2.35 Å. Both Fe(2)-As(2) bond lengths are 2.46 Å. In the third Fe site, Fe(3) is bonded in a 6-coordinate geometry to one As(3), one As(4), two equivalent As(1), and two equivalent As(2) atoms. The Fe(3)-As(3) bond length is 2.26 Å. The Fe(3)-As(4) bond length is 2.44 Å. Both Fe(3)-As(1) bond lengths are 2.39 Å. Both Fe(3)-As(2) bond lengths are 2.35 Å. Ni(1) is bonded in a 6-coordinate geometry to one As(1), one As(2), two equivalent As(3), and two equivalent As(4) atoms. The Ni(1)-As(1) bond length is 2.53 Å. The Ni(1)-As(2) bond length is 2.31 Å. Both Ni(1)-As(3) bond lengths are 2.41 Å. Both Ni(1)-As(4) bond lengths are 2.46 Å. There are four inequivalent As sites. In the first As site, As(1) is bonded in a 6-coordinate geometry to one Fe(1), two equivalent Fe(2), two equivalent Fe(3), and one Ni(1) atom. In the second As site, As(2) is bonded in a 6-coordinate geometry to one Fe(1), two equivalent Fe(2), two equivalent Fe(3), and one Ni(1) atom. In the third As site, As(3) is bonded in a 6-coordinate geometry to one Fe(2), one Fe(3), two equivalent Fe(1), and two equivalent Ni(1) atoms. In the fourth As site, As(4) is bonded in a 6-coordinate geometry to one Fe(2), one Fe(3), two equivalent Fe(1), and two equivalent Ni(1) atoms.