Er2NiAs2 crystallizes in the hexagonal P6_3mc space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 9-coordinate geometry to three equivalent Ni(1), three equivalent As(1), and three equivalent As(2) atoms. In the second Er site, Er(2) is bonded in a 9-coordinate geometry to three equivalent Ni(1), three equivalent As(1), and three equivalent As(2) atoms. Ni(1) is bonded in a 9-coordinate geometry to three equivalent Er(1), three equivalent Er(2), and three equivalent As(1) atoms. There are two inequivalent As sites. In the first As site, As(1) is bonded in a 9-coordinate geometry to three equivalent Er(1), three equivalent Er(2), and three equivalent Ni(1) atoms. In the second As site, As(2) is bonded to three equivalent Er(1) and three equivalent Er(2) atoms to form edge-sharing AsEr6 octahedra.
Er2NiAs2 crystallizes in the hexagonal P6_3mc space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 9-coordinate geometry to three equivalent Ni(1), three equivalent As(1), and three equivalent As(2) atoms. All Er(1)-Ni(1) bond lengths are 2.90 Å. All Er(1)-As(1) bond lengths are 3.04 Å. All Er(1)-As(2) bond lengths are 2.87 Å. In the second Er site, Er(2) is bonded in a 9-coordinate geometry to three equivalent Ni(1), three equivalent As(1), and three equivalent As(2) atoms. All Er(2)-Ni(1) bond lengths are 3.13 Å. All Er(2)-As(1) bond lengths are 2.99 Å. All Er(2)-As(2) bond lengths are 2.90 Å. Ni(1) is bonded in a 9-coordinate geometry to three equivalent Er(1), three equivalent Er(2), and three equivalent As(1) atoms. All Ni(1)-As(1) bond lengths are 2.38 Å. There are two inequivalent As sites. In the first As site, As(1) is bonded in a 9-coordinate geometry to three equivalent Er(1), three equivalent Er(2), and three equivalent Ni(1) atoms. In the second As site, As(2) is bonded to three equivalent Er(1) and three equivalent Er(2) atoms to form edge-sharing AsEr6 octahedra.