FeCoAs4 crystallizes in the monoclinic P2/m space group. Fe(1) is bonded to two equivalent As(2) and four equivalent As(1) atoms to form FeAs6 octahedra that share corners with eight equivalent Co(1)As6 octahedra and edges with two equivalent Fe(1)As6 octahedra. The corner-sharing octahedral tilt angles range from 53-54°. Co(1) is bonded to two equivalent As(1) and four equivalent As(2) atoms to form CoAs6 octahedra that share corners with eight equivalent Fe(1)As6 octahedra and edges with two equivalent Co(1)As6 octahedra. The corner-sharing octahedral tilt angles range from 53-54°. There are two inequivalent As sites. In the first As site, As(1) is bonded in a 3-coordinate geometry to two equivalent Fe(1) and one Co(1) atom. In the second As site, As(2) is bonded in a 3-coordinate geometry to one Fe(1) and two equivalent Co(1) atoms.
FeCoAs4 crystallizes in the monoclinic P2/m space group. Fe(1) is bonded to two equivalent As(2) and four equivalent As(1) atoms to form FeAs6 octahedra that share corners with eight equivalent Co(1)As6 octahedra and edges with two equivalent Fe(1)As6 octahedra. The corner-sharing octahedral tilt angles range from 53-54°. Both Fe(1)-As(2) bond lengths are 2.34 Å. All Fe(1)-As(1) bond lengths are 2.35 Å. Co(1) is bonded to two equivalent As(1) and four equivalent As(2) atoms to form CoAs6 octahedra that share corners with eight equivalent Fe(1)As6 octahedra and edges with two equivalent Co(1)As6 octahedra. The corner-sharing octahedral tilt angles range from 53-54°. Both Co(1)-As(1) bond lengths are 2.37 Å. All Co(1)-As(2) bond lengths are 2.38 Å. There are two inequivalent As sites. In the first As site, As(1) is bonded in a 3-coordinate geometry to two equivalent Fe(1) and one Co(1) atom. In the second As site, As(2) is bonded in a 3-coordinate geometry to one Fe(1) and two equivalent Co(1) atoms.