ErFe4B crystallizes in the hexagonal P6/mmm space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 18-coordinate geometry to six equivalent Fe(1) and twelve equivalent Fe(2) atoms. In the second Er site, Er(2) is bonded in a 18-coordinate geometry to twelve equivalent Fe(2) and six equivalent B(1) atoms. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 9-coordinate geometry to three equivalent Er(1) and six equivalent Fe(2) atoms. In the second Fe site, Fe(2) is bonded in a distorted L-shaped geometry to two equivalent Er(1), two equivalent Er(2), two equivalent Fe(1), and two equivalent B(1) atoms. B(1) is bonded in a 6-coordinate geometry to three equivalent Er(2) and six equivalent Fe(2) atoms.
ErFe4B crystallizes in the hexagonal P6/mmm space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded in a 18-coordinate geometry to six equivalent Fe(1) and twelve equivalent Fe(2) atoms. All Er(1)-Fe(1) bond lengths are 2.91 Å. All Er(1)-Fe(2) bond lengths are 3.21 Å. In the second Er site, Er(2) is bonded in a 18-coordinate geometry to twelve equivalent Fe(2) and six equivalent B(1) atoms. All Er(2)-Fe(2) bond lengths are 2.94 Å. All Er(2)-B(1) bond lengths are 2.91 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 9-coordinate geometry to three equivalent Er(1) and six equivalent Fe(2) atoms. All Fe(1)-Fe(2) bond lengths are 2.47 Å. In the second Fe site, Fe(2) is bonded in a distorted L-shaped geometry to two equivalent Er(1), two equivalent Er(2), two equivalent Fe(1), and two equivalent B(1) atoms. Both Fe(2)-B(1) bond lengths are 2.10 Å. B(1) is bonded in a 6-coordinate geometry to three equivalent Er(2) and six equivalent Fe(2) atoms.