FeCoAs crystallizes in the orthorhombic Pmm2 space group. There are four inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 5-coordinate geometry to one As(4), two equivalent As(2), and two equivalent As(3) atoms. In the second Fe site, Fe(2) is bonded in a 5-coordinate geometry to one As(4) and four equivalent As(3) atoms. In the third Fe site, Fe(3) is bonded in a 5-coordinate geometry to one As(1), two equivalent As(2), and two equivalent As(3) atoms. In the fourth Fe site, Fe(4) is bonded in a 4-coordinate geometry to two equivalent As(1) and two equivalent As(2) atoms. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded to one As(2), one As(3), and two equivalent As(4) atoms to form a mixture of distorted corner and edge-sharing CoAs4 tetrahedra. In the second Co site, Co(2) is bonded in a 5-coordinate geometry to one As(1) and four equivalent As(2) atoms. In the third Co site, Co(3) is bonded in a 4-coordinate geometry to two equivalent As(3) and two equivalent As(4) atoms. In the fourth Co site, Co(4) is bonded to one As(2), one As(3), and two equivalent As(1) atoms to form a mixture of distorted corner and edge-sharing CoAs4 tetrahedra. There are four inequivalent As sites. In the first As site, As(1) is bonded in a 9-coordinate geometry to two equivalent Fe(3), two equivalent Fe(4), one Co(2), and four equivalent Co(4) atoms. In the second As site, As(2) is bonded in a 9-coordinate geometry to one Fe(4), two equivalent Fe(1), two equivalent Fe(3), one Co(1), one Co(4), and two equivalent Co(2) atoms. In the third As site, As(3) is bonded in a 9-coordinate geometry to two equivalent Fe(1), two equivalent Fe(2), two equivalent Fe(3), one Co(1), one Co(3), and one Co(4) atom. In the fourth As site, As(4) is bonded in a 9-coordinate geometry to one Fe(2), two equivalent Fe(1), two equivalent Co(3), and four equivalent Co(1) atoms.
FeCoAs crystallizes in the orthorhombic Pmm2 space group. There are four inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 5-coordinate geometry to one As(4), two equivalent As(2), and two equivalent As(3) atoms. The Fe(1)-As(4) bond length is 2.43 Å. Both Fe(1)-As(2) bond lengths are 2.57 Å. Both Fe(1)-As(3) bond lengths are 2.56 Å. In the second Fe site, Fe(2) is bonded in a 5-coordinate geometry to one As(4) and four equivalent As(3) atoms. The Fe(2)-As(4) bond length is 2.43 Å. All Fe(2)-As(3) bond lengths are 2.55 Å. In the third Fe site, Fe(3) is bonded in a 5-coordinate geometry to one As(1), two equivalent As(2), and two equivalent As(3) atoms. The Fe(3)-As(1) bond length is 2.41 Å. Both Fe(3)-As(2) bond lengths are 2.58 Å. Both Fe(3)-As(3) bond lengths are 2.58 Å. In the fourth Fe site, Fe(4) is bonded in a 4-coordinate geometry to two equivalent As(1) and two equivalent As(2) atoms. Both Fe(4)-As(1) bond lengths are 2.36 Å. Both Fe(4)-As(2) bond lengths are 2.27 Å. There are four inequivalent Co sites. In the first Co site, Co(1) is bonded to one As(2), one As(3), and two equivalent As(4) atoms to form a mixture of distorted corner and edge-sharing CoAs4 tetrahedra. The Co(1)-As(2) bond length is 2.27 Å. The Co(1)-As(3) bond length is 2.28 Å. Both Co(1)-As(4) bond lengths are 2.36 Å. In the second Co site, Co(2) is bonded in a 5-coordinate geometry to one As(1) and four equivalent As(2) atoms. The Co(2)-As(1) bond length is 2.41 Å. All Co(2)-As(2) bond lengths are 2.54 Å. In the third Co site, Co(3) is bonded in a 4-coordinate geometry to two equivalent As(3) and two equivalent As(4) atoms. Both Co(3)-As(3) bond lengths are 2.27 Å. Both Co(3)-As(4) bond lengths are 2.37 Å. In the fourth Co site, Co(4) is bonded to one As(2), one As(3), and two equivalent As(1) atoms to form a mixture of distorted corner and edge-sharing CoAs4 tetrahedra. The Co(4)-As(2) bond length is 2.27 Å. The Co(4)-As(3) bond length is 2.26 Å. Both Co(4)-As(1) bond lengths are 2.35 Å. There are four inequivalent As sites. In the first As site, As(1) is bonded in a 9-coordinate geometry to two equivalent Fe(3), two equivalent Fe(4), one Co(2), and four equivalent Co(4) atoms. In the second As site, As(2) is bonded in a 9-coordinate geometry to one Fe(4), two equivalent Fe(1), two equivalent Fe(3), one Co(1), one Co(4), and two equivalent Co(2) atoms. In the third As site, As(3) is bonded in a 9-coordinate geometry to two equivalent Fe(1), two equivalent Fe(2), two equivalent Fe(3), one Co(1), one Co(3), and one Co(4) atom. In the fourth As site, As(4) is bonded in a 9-coordinate geometry to one Fe(2), two equivalent Fe(1), two equivalent Co(3), and four equivalent Co(1) atoms.